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tim... January 11th 19 07:52 PM

how hot do you run you CH boiler
 
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer period
than a higher temperature for a shorter period

I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"

and the completely bogus "the temperature of the water in the radiators is
set by the TRVs not the boiler temp. I couldn't persuade the guy that he
was taking bollox, he played the "I'm the experience heating engineer card
and I know better than you" card. ****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

tim












Andy Bennet January 11th 19 08:08 PM

how hot do you run you CH boiler
 
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer
period than a higher temperature for a shorter period

I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"

and the completely bogus "the temperature of the water in the radiators
is set by the TRVs not the boiler temp.Â* I couldn't persuade the guy
that he was taking bollox, he played the "I'm the experience heating
engineer card and I know better than you" card.Â* ****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

tim


Electric boiler so not concerned with condenser temperature bollox,
always 100% efficient

.. Run ours at 80C normally, if really cold ramp it up to 85C on the
basis of highest coupling efficiency between rads and air. Fastest
heatup. No kids so rad temp not an issue.



John Rumm January 11th 19 10:30 PM

how hot do you run you CH boiler
 
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as


Indeed...

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer
period than a higher temperature for a shorter period


It might be required in particularly cold weather, but most of the time
you will be able to use less.


I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"


You will most heat recovered from the condenser when the return
temperature is below about 54 degrees (the dew point of the flue gasses).

and the completely bogus "the temperature of the water in the radiators
is set by the TRVs not the boiler temp.Â* I couldn't persuade the guy
that he was taking bollox, he played the "I'm the experience heating
engineer card and I know better than you" card.Â* ****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do


I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs as
cool as it thinks it can get away with and still be able to reach the
target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the rate
of heat loss of the building).

Currently the external temp is 6.5 deg C, and the flow temp is running
at 54 deg. If it were to go well below 0, then it might push the flow
temp up into the 70s. When its milder it might run flow temps down in
the 40s.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

[email protected] January 11th 19 11:25 PM

how hot do you run you CH boiler
 
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as


Indeed...

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer
period than a higher temperature for a shorter period


It might be required in particularly cold weather, but most of the time
you will be able to use less.


I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"


You will most heat recovered from the condenser when the return
temperature is below about 54 degrees (the dew point of the flue gasses).

and the completely bogus "the temperature of the water in the
radiators is set by the TRVs not the boiler temp.Â* I couldn't persuade
the guy that he was taking bollox, he played the "I'm the experience
heating engineer card and I know better than you" card.Â* ****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do


I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs as
cool as it thinks it can get away with and still be able to reach the
target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the rate
of heat loss of the building).

Currently the external temp is 6.5 deg C, and the flow temp is running
at 54 deg. If it were to go well below 0, then it might push the flow
temp up into the 70s. When its milder it might run flow temps down in
the 40s.


I thought the advice was to heat DHW to 60 degrees to avoid the risk of
legionella, and that's not going to happen if the boiler's running at a
lower temp.

Tim+[_5_] January 11th 19 11:35 PM

how hot do you run you CH boiler
 
wrote:


I thought the advice was to heat DHW to 60 degrees to avoid the risk of
legionella, and that's not going to happen if the boiler's running at a
lower temp.


That may be true, but in practice I dont think Legionella has ever proved
to be a problem in domestic systems.

Tim



--
Please don't feed the trolls

[email protected] January 11th 19 11:42 PM

how hot do you run you CH boiler
 
On Friday, 11 January 2019 18:54:03 UTC, tim... wrote:

I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer period
than a higher temperature for a shorter period

I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"

and the completely bogus "the temperature of the water in the radiators is
set by the TRVs not the boiler temp. I couldn't persuade the guy that he
was taking bollox, he played the "I'm the experience heating engineer card
and I know better than you" card. ****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

tim


The only realistic answer is to run it as hot as is necessary to provide enough heating. Cooler means more boiler efficiency, hotter means more rad output. The required target temp varies from one house & install to another, and varies with the weather.


NT

Max Demian January 12th 19 12:33 AM

how hot do you run you CH boiler
 
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer
period than a higher temperature for a shorter period

I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"


The instruction manual for my Ideal says that the 'e' setting is best
for condensing, which is quite hot. I don't understand this as I would
have thought that the cooler the returning water temperature the more
condensing.

I use a much lower temperature as I don't have a room thermostat and the
TRVs are fiddly and don't seem to keep the air temperature constant.

--
Max Demian

Harry Bloomfield[_3_] January 12th 19 12:48 AM

how hot do you run you CH boiler
 
tim... pretended :
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as


I have an opened vented system, with stored HW and the house is heated
by the one boiler, installed new last March. A Vailant ECOfit Pure 418.
We like the stored water to be good and hot, the boiler only has one
temperature setting available for its output temperature - so I have it
set at its max, of 75C, in order to meet our HW needs. The house
heating would be satisfied by a lower boiler temperature around 60C and
it would be more gas efficient, but unless I manually manage the
temperature setting I am stuck with the less efficient 75C.

I even tried to find a way to fool the boiler into working at a lower
output temperature, by adding a separate bi-metal stat on the boiler
output pipe to CH only, set at 60C, to shut it down at that temperature
- as heating satisfied. That was a miserable failure, in that the
boiler constantly cycled on/off via the stat, whilst ever the room stat
indicated a demand, rather than modulating its output down - as it
would on its own as it neared its 75C setting.

If anyone knows a workaround, to allow split boiler output temperatures
on this boiler - do let me know please.

RJH[_2_] January 12th 19 01:55 AM

how hot do you run you CH boiler
 
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

snip

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do


I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs as
cool as it thinks it can get away with and still be able to reach the
target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the rate
of heat loss of the building).


I don't follow how that can work properly, as for most homes different
rooms will have a different 'curve'. Or does tweaking the TRV compensate?


--
Cheers, Rob

RJH[_2_] January 12th 19 01:59 AM

how hot do you run you CH boiler
 
On 11/01/2019 23:33, Max Demian wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer
period than a higher temperature for a shorter period

I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"


The instruction manual for my Ideal says that the 'e' setting is best
for condensing, which is quite hot. I don't understand this as I would
have thought that the cooler the returning water temperature the more
condensing.


My understanding of the 'e' mark on my Ideal boiler's central heating
temperature control is that any setting above is non-condensing. Any
setting below and the boiler's condensing.

I use a much lower temperature as I don't have a room thermostat and the
TRVs are fiddly and don't seem to keep the air temperature constant.



--
Cheers, Rob

John Rumm January 12th 19 07:56 AM

how hot do you run you CH boiler
 
On 11/01/2019 22:25, wrote:
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as


Indeed...

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile
will result from having the radiators at the lower temperate for
longer period than a higher temperature for a shorter period


It might be required in particularly cold weather, but most of the
time you will be able to use less.


I tried to explain this but was met with

"The recommended temperature is required for the condenser to have
any effect"


You will most heat recovered from the condenser when the return
temperature is below about 54 degrees (the dew point of the flue gasses).

and the completely bogus "the temperature of the water in the
radiators is set by the TRVs not the boiler temp.Â* I couldn't
persuade the guy that he was taking bollox, he played the "I'm the
experience heating engineer card and I know better than you" card.Â* ****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do


I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs
as cool as it thinks it can get away with and still be able to reach
the target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the rate
of heat loss of the building).

Currently the external temp is 6.5 deg C, and the flow temp is running
at 54 deg. If it were to go well below 0, then it might push the flow
temp up into the 70s. When its milder it might run flow temps down in
the 40s.


I thought the advice was to heat DHW to 60 degrees to avoid the risk of
legionella, and that's not going to happen if the boiler's running at a
lower temp.


Oddly enough when I typed the reply above, I originally included
discussion of DHW, however deleted it since I thought it was detail not
required to answer the OP.

Yup, the system runs higher flow temperatures for DHW reheat (or at
least the later stages of them). It will modulate the flow temp during
the process to achieve maximum condensation efficiency, while also
ensuring good heat transfer rates). The coil in the cylinder will allow
a recharge at a maximum rate of around 20 - 22kW - just a little bit
less than the maximum output of the boiler.

Its a S plan+ system, but never actually runs he rads and DHW at the
same time.

I have it set to heat to 60 degrees for six days a week, and then it
runs an anti legionella cycle one day a week, where it heats it to 70.

There is a TMV on the output of the cylinder to limit the maximum DHW
temperature delivered to the points of use.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd -
http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

harry January 12th 19 08:12 AM

how hot do you run you CH boiler
 
On Friday, 11 January 2019 22:35:12 UTC, Tim+ wrote:
wrote:


I thought the advice was to heat DHW to 60 degrees to avoid the risk of
legionella, and that's not going to happen if the boiler's running at a
lower temp.


That may be true, but in practice I dont think Legionella has ever proved
to be a problem in domestic systems.



Oh yes it has. Plenty of people have died.
https://www.dailymail.co.uk/news/art...ish-homes.html

harry January 12th 19 08:16 AM

how hot do you run you CH boiler
 
On Friday, 11 January 2019 23:33:44 UTC, Max Demian wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer
period than a higher temperature for a shorter period

I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"


The instruction manual for my Ideal says that the 'e' setting is best
for condensing, which is quite hot. I don't understand this as I would
have thought that the cooler the returning water temperature the more
condensing.

I use a much lower temperature as I don't have a room thermostat and the
TRVs are fiddly and don't seem to keep the air temperature constant.

--
Max Demian


TRVs don't work. They are more influenced by the nearby radiator temperature than the room air temp.
You can get them with remote sensors. They work.

John Rumm January 12th 19 08:30 AM

how hot do you run you CH boiler
 
On 12/01/2019 00:55, RJH wrote:
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

snip

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do


I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs
as cool as it thinks it can get away with and still be able to reach
the target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the rate
of heat loss of the building).


I don't follow how that can work properly, as for most homes different
rooms will have a different 'curve'. Or does tweaking the TRV compensate?


It seems to work well enough in practice. Each room also has a TRV, and
I have the place split into two zones; upstairs and downstairs, so that
will account for some variation.

It needs a little bit of experimentation to set the profile the first
time - basically waiting for colder days and seeing if the system still
heats the place comfortably and quickly enough. If it doesn't, then you
just tweak it up to a steeper curve. It also helps if you have
appropriate rad sizes for the rooms, and the system is balanced.

The response curves look like:

http://wiki.diyfaq.org.uk/index.php/...tingCurve1.png

IIRC the system defaults to the 1.2 line. If you live in a super
insulted place / particularly sheltered location then you would tweak
down. In my case (exposed location - solid wall construction), I needed
to go up. I found the 1.8 curve worked well.

The system is also smart enough to automatically shift the response
curve vertically based on the currently demanded internal target
temperature[1]:

http://wiki.diyfaq.org.uk/index.php/...tingCurve2.png

So if you tweak the room temp up or down during the day (or have
different times programmed with different set point temps), then it can
vary the flow temperature to match the requirement.

[1] Note that all the system temperatures sensors (internal downstairs,
internal upstairs, DHW cylinder, and external) are digitized and
processed as actual temperatures, not just as on/off "call for heat"
style demands.



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

John Rumm January 12th 19 08:35 AM

how hot do you run you CH boiler
 
On 11/01/2019 22:42, wrote:
On Friday, 11 January 2019 18:54:03 UTC, tim... wrote:

I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

1) it makes the radiators too hot to touch 2) basic thermodynamics
suggest that a better temperature profile will result from having
the radiators at the lower temperate for longer period than a
higher temperature for a shorter period

I tried to explain this but was met with

"The recommended temperature is required for the condenser to have
any effect"

and the completely bogus "the temperature of the water in the
radiators is set by the TRVs not the boiler temp. I couldn't
persuade the guy that he was taking bollox, he played the "I'm the
experience heating engineer card and I know better than you" card.
****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

tim


The only realistic answer is to run it as hot as is necessary to
provide enough heating. Cooler means more boiler efficiency, hotter
means more rad output. The required target temp varies from one house
& install to another, and varies with the weather.


yup, spot on.

It leaves three options:

set and forget - chose a high flow temp that meets the worst case, and
accept that you will be running with less efficiency / comfort for most
of the year.

manual - adjust the flow temperature yourself in response to
particularly cold days - probably works quite well for users who are
clued up enough to understand the requirement.

automatic - use weather compensation to "close the loop".


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd -
http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

David Wade[_2_] January 12th 19 08:51 AM

how hot do you run you CH boiler
 
On 11/01/2019 23:33, Max Demian wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer
period than a higher temperature for a shorter period

I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"


The instruction manual for my Ideal says that the 'e' setting is best
for condensing, which is quite hot. I don't understand this as I would
have thought that the cooler the returning water temperature the more
condensing.

I use a much lower temperature as I don't have a room thermostat and the
TRVs are fiddly and don't seem to keep the air temperature constant.

If your boiler allows external timers consider getting a TADO or Drayton
Wiser (Or just wireless TRVs and a Reaspberry PI if you are the
adventurous type). Lets you see what temp the TRVs think the room is at.

Dave

John Rumm January 12th 19 08:54 AM

how hot do you run you CH boiler
 
On 11/01/2019 23:48, Harry Bloomfield wrote:
tim... pretended :
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as


I have an opened vented system, with stored HW and the house is heated
by the one boiler, installed new last March. A Vailant ECOfit Pure 418.
We like the stored water to be good and hot, the boiler only has one
temperature setting available for its output temperature - so I have it
set at its max, of 75C, in order to meet our HW needs. The house heating
would be satisfied by a lower boiler temperature around 60C and it would
be more gas efficient, but unless I manually manage the temperature
setting I am stuck with the less efficient 75C.

I even tried to find a way to fool the boiler into working at a lower
output temperature, by adding a separate bi-metal stat on the boiler
output pipe to CH only, set at 60C, to shut it down at that temperature
- as heating satisfied. That was a miserable failure, in that the boiler
constantly cycled on/off via the stat, whilst ever the room stat
indicated a demand, rather than modulating its output down - as it would
on its own as it neared its 75C setting.

If anyone knows a workaround, to allow split boiler output temperatures
on this boiler - do let me know please.


IME many of the Vaillant boilers do support split temperature operation,
but it does depends on what controls you have them paired with.

The 400 series Vaillant I did (probably previous model range, since this
was = 12 years ago), actually had separate knobs on the front for CH
and DHW flow temperatures. Although that was retrofitted into system
with traditional controls that could not distinguish between the source
of the call for heat - hence the DHW control never came into play and it
ran like your system does.

The blurb on their web site:

https://www.vaillant.co.uk/for-insta...ler-26116.html

Seems to suggest its compatible with the VRC 700 weather compensating
controls, so that ought to allow split temperature as well.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Harry Bloomfield[_3_] January 12th 19 09:28 AM

how hot do you run you CH boiler
 
Max Demian explained :
I use a much lower temperature as I don't have a room thermostat and the TRVs
are fiddly and don't seem to keep the air temperature constant.


That is at odds with my own findings, since installing TRV's last
March, but I do have a room stat, in the hall and no TRV on just that
one rad.

I tried setting the TRV's up in March for each room, but there wasn't
much need for heat at all then. I found it better to set them once the
cold weather arrived this winter. Having gradually tweaked each to a
comfortable temperature, they work pretty well. Working on just a room
stat, the temperature variation was quite noticeable as the boiler
kicked in and out on just the room stat..

Harry Bloomfield[_3_] January 12th 19 09:38 AM

how hot do you run you CH boiler
 
John Rumm pretended :
It needs a little bit of experimentation to set the profile the first time -
basically waiting for colder days and seeing if the system still heats the
place comfortably and quickly enough. If it doesn't, then you just tweak it
up to a steeper curve. It also helps if you have appropriate rad sizes for
the rooms, and the system is balanced.


Balanced?

I have always assumed there was no need to balance a system, where
TRV's are installed.

Harry Bloomfield[_3_] January 12th 19 09:49 AM

how hot do you run you CH boiler
 
It happens that John Rumm formulated :
set and forget - chose a high flow temp that meets the worst case, and accept
that you will be running with less efficiency / comfort for most of the year.


Which is what I have done. The TRV's prevent the rads getting hotter
than needed for each room, except when the heating is first put on with
the house 'cold'. In quotes, because it never gets truly cold.

To mitigate turning the heating on from cold and the room temperature
over shooting, I tend to nudge the room stat up in a series of steps
over several minutes.

tim... January 12th 19 09:56 AM

how hot do you run you CH boiler
 


wrote in message
...
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as


Indeed...

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer
period than a higher temperature for a shorter period


It might be required in particularly cold weather, but most of the time
you will be able to use less.


I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"


You will most heat recovered from the condenser when the return
temperature is below about 54 degrees (the dew point of the flue gasses).

and the completely bogus "the temperature of the water in the radiators
is set by the TRVs not the boiler temp. I couldn't persuade the guy
that he was taking bollox, he played the "I'm the experience heating
engineer card and I know better than you" card. ****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do


I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs as
cool as it thinks it can get away with and still be able to reach the
target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the rate of
heat loss of the building).

Currently the external temp is 6.5 deg C, and the flow temp is running at
54 deg. If it were to go well below 0, then it might push the flow temp
up into the 70s. When its milder it might run flow temps down in the 40s.


I thought the advice was to heat DHW to 60 degrees to avoid the risk of
legionella, and that's not going to happen if the boiler's running at a
lower temp.


the temp for the hot water and CH system are set independently in a combi




tim... January 12th 19 10:03 AM

how hot do you run you CH boiler
 


wrote in message
...
On Friday, 11 January 2019 18:54:03 UTC, tim... wrote:

I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer period
than a higher temperature for a shorter period

I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"

and the completely bogus "the temperature of the water in the radiators
is
set by the TRVs not the boiler temp. I couldn't persuade the guy that he
was taking bollox, he played the "I'm the experience heating engineer
card
and I know better than you" card. ****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

tim


The only realistic answer is to run it as hot as is necessary to provide
enough heating. Cooler means more boiler efficiency, hotter means more rad
output. The required target temp varies from one house & install to
another, and varies with the weather.


The house, um flat, is well insulated

I have been living in it part time for the past 6 weeks with no heating at
all.

It was a bit on the cold side but not unbearable

Now that the heating is working, it will need to provide a very small amount
of heat to keep the place warm

I am more interested in the effect on the reliability of the boiler of
setting a low temp, as there is no possibility that such a setting wont warm
the house.

tim




tim... January 12th 19 10:06 AM

how hot do you run you CH boiler
 


"Harry Bloomfield" wrote in message
...
tim... pretended :
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as


I have an opened vented system, with stored HW and the house is heated by
the one boiler, installed new last March. A Vailant ECOfit Pure 418. We
like the stored water to be good and hot, the boiler only has one
temperature setting available for its output temperature - so I have it
set at its max, of 75C, in order to meet our HW needs.


not something that is a consideration with a combi




Harry Bloomfield[_3_] January 12th 19 10:09 AM

how hot do you run you CH boiler
 
After serious thinking harry wrote :
TRVs don't work. They are more influenced by the nearby radiator temperature
than the room air temp.
You can get them with remote sensors. They work.


They work absolutely fine here, once the heating has been on for a
while and the system has settled down. I am able to log/graph room
temperatures and once temperature is achieved, I only see variations of
around 0.5C in the graphs. What TRV's or any type of stat cannot cope
with is the overshoot, when the heating is suddenly turned on, or the
stat suddenly turned up to a much higher setting.

tim... January 12th 19 10:10 AM

how hot do you run you CH boiler
 


"Harry Bloomfield" wrote in message
...
John Rumm pretended :
It needs a little bit of experimentation to set the profile the first
time - basically waiting for colder days and seeing if the system still
heats the place comfortably and quickly enough. If it doesn't, then you
just tweak it up to a steeper curve. It also helps if you have
appropriate rad sizes for the rooms, and the system is balanced.


Balanced?

I have always assumed there was no need to balance a system, where TRV's
are installed.


if TRVs can be set to reliably keep a room at, say 20 degrees, then it
doesn't

but if they can't, then it does

I'm about to find out if the first line is true, because it is clear than my
new systems is not balanced.

As it is currently set, the lounge is like a sauna, and the rest of the
house still cool.

I actually don't have a problem with the latter, it's the former that's the
issue

tim




[email protected] January 12th 19 10:28 AM

how hot do you run you CH boiler
 
On 12/01/2019 08:56, tim... wrote:


wrote in message
...
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

Indeed...

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile
will result from having the radiators at the lower temperate for
longer period than a higher temperature for a shorter period

It might be required in particularly cold weather, but most of the
time you will be able to use less.


I tried to explain this but was met with

"The recommended temperature is required for the condenser to have
any effect"

You will most heat recovered from the condenser when the return
temperature is below about 54 degrees (the dew point of the flue
gasses).

and the completely bogus "the temperature of the water in the
radiators is set by the TRVs not the boiler temp.Â* I couldn't
persuade the guy that he was taking bollox, he played the "I'm the
experience heating engineer card and I know better than you" card.
****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs
as cool as it thinks it can get away with and still be able to reach
the target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the
rate of heat loss of the building).

Currently the external temp is 6.5 deg C, and the flow temp is
running at 54 deg. If it were to go well below 0, then it might push
the flow temp up into the 70s. When its milder it might run flow
temps down in the 40s.


I thought the advice was to heat DHW to 60 degrees to avoid the risk
of legionella, and that's not going to happen if the boiler's running
at a lower temp.


the temp for the hot water and CH system are set independently in a combi



I was replying to John (but had forgotten about combis)

Harry Bloomfield[_3_] January 12th 19 10:28 AM

how hot do you run you CH boiler
 
John Rumm formulated the question :
IME many of the Vaillant boilers do support split temperature operation, but
it does depends on what controls you have them paired with.

The 400 series Vaillant I did (probably previous model range, since this was
= 12 years ago), actually had separate knobs on the front for CH and DHW
flow temperatures. Although that was retrofitted into system with
traditional controls that could not distinguish between the source of the
call for heat - hence the DHW control never came into play and it ran like
your system does.


The blurb on their web site:

https://www.vaillant.co.uk/for-insta...ler-26116.html

Seems to suggest its compatible with the VRC 700 weather compensating
controls, so that ought to allow split temperature as well.


I have studied it and not found any obvious way to split the
temperature. I even spoke to Vailant and they confirmed there was no
way it could be done.

[email protected] January 12th 19 11:03 AM

how hot do you run you CH boiler
 
On 12/01/2019 06:56, John Rumm wrote:
On 11/01/2019 22:25, wrote:
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

Indeed...

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile
will result from having the radiators at the lower temperate for
longer period than a higher temperature for a shorter period

It might be required in particularly cold weather, but most of the
time you will be able to use less.


I tried to explain this but was met with

"The recommended temperature is required for the condenser to have
any effect"

You will most heat recovered from the condenser when the return
temperature is below about 54 degrees (the dew point of the flue
gasses).

and the completely bogus "the temperature of the water in the
radiators is set by the TRVs not the boiler temp.Â* I couldn't
persuade the guy that he was taking bollox, he played the "I'm the
experience heating engineer card and I know better than you" card.
****

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs
as cool as it thinks it can get away with and still be able to reach
the target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the
rate of heat loss of the building).

Currently the external temp is 6.5 deg C, and the flow temp is
running at 54 deg. If it were to go well below 0, then it might push
the flow temp up into the 70s. When its milder it might run flow
temps down in the 40s.


I thought the advice was to heat DHW to 60 degrees to avoid the risk
of legionella, and that's not going to happen if the boiler's running
at a lower temp.


Oddly enough when I typed the reply above, I originally included
discussion of DHW, however deleted it since I thought it was detail not
required to answer the OP.

Yup, the system runs higher flow temperatures for DHW reheat (or at
least the later stages of them). It will modulate the flow temp during
the process to achieve maximum condensation efficiency, while also
ensuring good heat transfer rates). The coil in the cylinder will allow
a recharge at a maximum rate of around 20 - 22kW - just a little bit
less than the maximum output of the boiler.

Does the boiler have an input to tell it that it's heating the DHW, or
is the flow temperature adjusted automagically based on flow and return
characteristics?
I'm fairly certain that weather compensation isn't available for my W-B
Greenstar 32/50 boiler, according to the book the manual adjustment
range is 60-82C.

Its a S plan+ system, but never actually runs he rads and DHW at the
same time.

My system is S+, but with Honeywell Evohome controls. Each room is a
unique zone (2 zones in the bathrooms), with its own thermostat and time
schedule. There is no "house" stat; the rads and DHW all operate
independently of one another.

I have it set to heat to 60 degrees for six days a week, and then it
runs an anti legionella cycle one day a week, where it heats it to 70.

Raising the temp to 70C for one day per week, and keeping it at 50C
(say) at other times, seems like a damned good idea. I'll make the
changes next time I'm fiddling with the settings.

There is a TMV on the output of the cylinder to limit the maximum DHW
temperature delivered to the points of use.

I thought about a TMV when I planned the system but decided not to
bother - perhaps an error.



dennis@home[_6_] January 12th 19 11:04 AM

how hot do you run you CH boiler
 
On 12/01/2019 09:10, tim... wrote:


"Harry Bloomfield" wrote in message
...
John Rumm pretended :
It needs a little bit of experimentation to set the profile the first
time - basically waiting for colder days and seeing if the system
still heats the place comfortably and quickly enough. If it doesn't,
then you just tweak it up to a steeper curve. It also helps if you
have appropriate rad sizes for the rooms, and the system is balanced.


Balanced?

I have always assumed there was no need to balance a system, where
TRV's are installed.


if TRVs can be set to reliably keep a room at, say 20 degrees, then it
doesn't

but if they can't, then it does

I'm about to find out if the first line is true, because it is clear
than my new systems is not balanced.

As it is currently set, the lounge is like a sauna, and the rest of the
house still cool.

I actually don't have a problem with the latter, it's the former that's
the issue

tim




Where is the room stat?

That is the big problem with TRVs, you have to have the system run
whenever any rad wants heat and its difficult to impossible with only
one room stat.

Its a pretty crap way of doing it really.


I have separate timer+stats on all the main rooms with 2 port valves.
The valves have switches on them so they turn the boiler on if any of
them is open.

It costs more than TRVs but also saves money.

The plumbers have trouble understanding stuff like that which is why
they always go for TRVs as a second best option.

RJH[_2_] January 12th 19 11:19 AM

how hot do you run you CH boiler
 
On 11/01/2019 23:33, Max Demian wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

Which I thought far too high, as

1) it makes the radiators too hot to touch
2) basic thermodynamics suggest that a better temperature profile will
result from having the radiators at the lower temperate for longer
period than a higher temperature for a shorter period

I tried to explain this but was met with

"The recommended temperature is required for the condenser to have any
effect"


The instruction manual for my Ideal says that the 'e' setting is best
for condensing, which is quite hot. I don't understand this as I would
have thought that the cooler the returning water temperature the more
condensing.


Just found the manual for my Ideal Logic:

"The Logic + Combi is a high efficiency combination boiler which is most
efficient when operating in condensing mode.

The boiler will operate in this mode if the CH temperature control (C)
is set to the €˜e position (economy mode) or below. This control should
be set to a maximum for very cold periods".

I use a much lower temperature as I don't have a room thermostat and the
TRVs are fiddly and don't seem to keep the air temperature constant.



--
Cheers, Rob

Tim Watts[_5_] January 12th 19 11:23 AM

how hot do you run you CH boiler
 
On 11/01/2019 21:30, John Rumm wrote:
I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs as
cool as it thinks it can get away with and still be able to reach the
target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the rate
of heat loss of the building).

Currently the external temp is 6.5 deg C, and the flow temp is running
at 54 deg. If it were to go well below 0, then it might push the flow
temp up into the 70s. When its milder it might run flow temps down in
the 40s.


Annoying Worcester do not have a simple weather comp option for theirs
(you have to have the fancy controller and that precludes using your own
heating controller, according to them).

I oversized my rads as much as possible and I have been able to run on
64/54 in deep winter and 55/45 in the less cold parts of the year.


--
Email does not work

RJH[_2_] January 12th 19 11:25 AM

how hot do you run you CH boiler
 
On 12/01/2019 07:30, John Rumm wrote:
On 12/01/2019 00:55, RJH wrote:
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:
I had a new Combi fitted today (in the to-be-moved-to house).

Fitters told me that I should run this at 74 degrees.

snip

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

I have weather compensation on mine, and so it chooses its own
temperature based on the outside temp. Basically that means its runs
as cool as it thinks it can get away with and still be able to reach
the target set point temperature in a reasonable amount of time. (the
relationship is set by choosing a mapping curve that reflects the
rate of heat loss of the building).


I don't follow how that can work properly, as for most homes different
rooms will have a different 'curve'. Or does tweaking the TRV compensate?


It seems to work well enough in practice. Each room also has a TRV, and
I have the place split into two zones; upstairs and downstairs, so that
will account for some variation.

It needs a little bit of experimentation to set the profile the first
time - basically waiting for colder days and seeing if the system still
heats the place comfortably and quickly enough. If it doesn't, then you
just tweak it up to a steeper curve. It also helps if you have
appropriate rad sizes for the rooms, and the system is balanced.

The response curves look like:

http://wiki.diyfaq.org.uk/index.php/...tingCurve1.png

IIRC the system defaults to the 1.2 line. If you live in a super
insulted place / particularly sheltered location then you would tweak
down. In my case (exposed location - solid wall construction), I needed
to go up. I found the 1.8 curve worked well.

The system is also smart enough to automatically shift the response
curve vertically based on the currently demanded internal target
temperature[1]:

http://wiki.diyfaq.org.uk/index.php/...tingCurve2.png

So if you tweak the room temp up or down during the day (or have
different times programmed with different set point temps), then it can
vary the flow temperature to match the requirement.

[1] Note that all the system temperatures sensors (internal downstairs,
internal upstairs, DHW cylinder, and external) are digitized and
processed as actual temperatures, not just as on/off "call for heat"
style demands.


Thanks for that, interesting. And I hadn't realised such systems had a
collection of sensors.

OT but loosely relevant, I use my CH as 2 zones - upstairs and
downstairs. I'm really not going to replumb to add a properly zones
system, and I was wondering if it's possible to isolate the upstairs
zone with a three way motorised valve - simply cutting out the upstairs
'circuit'.

A single switch would be easier than faffing about with 4 TRVs each evening.

--
Cheers, Rob

Harry Bloomfield[_3_] January 12th 19 11:32 AM

how hot do you run you CH boiler
 
on 12/01/2019, dennis@home supposed :
Where is the room stat?


My stat is in the hall and it is generally set to a lower temperature
than we desire in the living room next to it.


That is the big problem with TRVs, you have to have the system run whenever
any rad wants heat and its difficult to impossible with only one room stat.


Generally, if our hall is below temperature, other parts of the house
will be too. So in practise it works pretty well.


Its a pretty crap way of doing it really.


It is a compromise of cost versus ideal with considerable extra
complexity. Ideal is a zone per room, a temperature sensor per room and
the means to use the data/ decide which rooms should be what
temperature at what times of day, maybe to include occupation sensors.
The boiler coming on if any zone requires heat input.

dennis@home[_6_] January 12th 19 11:55 AM

how hot do you run you CH boiler
 
On 12/01/2019 09:09, Harry Bloomfield wrote:
After serious thinking harry wrote :
TRVs don't work. They are more influenced by the nearby radiator
temperature than the room air temp.
You can get them with remote sensors. They work.


They work absolutely fine here, once the heating has been on for a while
and the system has settled down. I am able to log/graph room
temperatures and once temperature is achieved, I only see variations of
around 0.5C in the graphs. What TRV's or any type of stat cannot cope
with is the overshoot, when the heating is suddenly turned on, or the
stat suddenly turned up to a much higher setting.


That's not a stat problem that's too much heat capacity in the radiators.

The stat stops the flow but the stuff in the rad is too hot.

You need to have low water content rads.


dennis@home[_6_] January 12th 19 12:01 PM

how hot do you run you CH boiler
 
On 11/01/2019 23:48, Harry Bloomfield wrote:


If anyone knows a workaround, to allow split boiler output temperatures
on this boiler - do let me know please.


IIRC one of the add on controllers allows for different temps when
running HW and heating but I don't recall which.

Harry Bloomfield[_3_] January 12th 19 12:33 PM

how hot do you run you CH boiler
 
dennis@home explained :
That's not a stat problem that's too much heat capacity in the radiators.

The stat stops the flow but the stuff in the rad is too hot.

You need to have low water content rads.


I agree, it was originally installed when the place had a much higher
heat loss. Single glazed, no CWI, not much insulation in the roof and
quite air leaky. But its a cost v benefit v need. Only one rad has
needed to be changed and that swapped for one half the capacity, in the
hall. The original boiler was around 32Kw, the new one 18Kw. The guy I
got to install it, even suggested that was probably borderline too big,
but I specced it.

Too much capacity has the advantage that - Nudge the stat up a couple
of degrees and it hits the selected new temperature very quickly. Then
once up to temperature, it barely ticks over.

Harry Bloomfield[_3_] January 12th 19 12:39 PM

how hot do you run you CH boiler
 
dennis@home brought next idea :
IIRC one of the add on controllers allows for different temps when running HW
and heating but I don't recall which.


It would have to be something which interacted directly with the boiler
and Vailant said there was nothing able to do that, when I spoke to
them. The boiler has the built in interfaces for the fancier control
systems, I understand, but little detail to be found about these extra
systems.

John Rumm January 12th 19 12:59 PM

how hot do you run you CH boiler
 
On 12/01/2019 10:03, wrote:
On 12/01/2019 06:56, John Rumm wrote:
On 11/01/2019 22:25,
wrote:
On 11/01/2019 21:30, John Rumm wrote:
On 11/01/2019 18:52, tim... wrote:


I had a new Combi fitted today (in the to-be-moved-to house).


[snip]

Anyhow, at my current house it is 55 and works perfectly well

what do you guys/galls do

I have weather compensation on mine, and so it chooses its own

[snip]

Currently the external temp is 6.5 deg C, and the flow temp is
running at 54 deg. If it were to go well below 0, then it might push
the flow temp up into the 70s. When its milder it might run flow
temps down in the 40s.


I thought the advice was to heat DHW to 60 degrees to avoid the risk
of legionella, and that's not going to happen if the boiler's running
at a lower temp.


Oddly enough when I typed the reply above, I originally included
discussion of DHW, however deleted it since I thought it was detail
not required to answer the OP.

Yup, the system runs higher flow temperatures for DHW reheat (or at
least the later stages of them). It will modulate the flow temp during
the process to achieve maximum condensation efficiency, while also
ensuring good heat transfer rates). The coil in the cylinder will
allow a recharge at a maximum rate of around 20 - 22kW - just a little
bit less than the maximum output of the boiler.


Does the boiler have an input to tell it that it's heating the DHW, or
is the flow temperature adjusted automagically based on flow and return
characteristics?


Yes ;-)

The boiler knows what it is heating - you get a Tap logo pop up on its
LCD rather than a radiator logo. The information is conveyed over its
eBus rather than with a discrete input.

Also like many boilers, it can adjust its power output based on a number
of criteria including flow and return temps etc.

I'm fairly certain that weather compensation isn't available for my W-B
Greenstar 32/50 boiler, according to the book the manual adjustment
range is 60-82C.


ISTR that when I was looking for system boiler's that could do split
temp, there were some options for some of the WB boilers.

(I also considered paring a combi with an unvented cylinder, so one
could have fast potable DHW to the kitchen which is on a long pipe run)


Its a S plan+ system, but never actually runs he rads and DHW at the
same time.

My system is S+, but with Honeywell Evohome controls. Each room is a
unique zone (2 zones in the bathrooms), with its own thermostat and time
schedule. There is no "house" stat; the rads and DHW all operate
independently of one another.

I have it set to heat to 60 degrees for six days a week, and then it
runs an anti legionella cycle one day a week, where it heats it to 70.

Raising the temp to 70C for one day per week, and keeping it at 50C
(say) at other times, seems like a damned good idea. I'll make the
changes next time I'm fiddling with the settings.

There is a TMV on the output of the cylinder to limit the maximum DHW
temperature delivered to the points of use.

I thought about a TMV when I planned the system but decided not to
bother - perhaps an error.


I was not that keen on the idea that some times it would otherwise
deliver 70 degree water to the taps.

Having a TMV on the cylinder output is a bit of a compromise, since it
means you don't have the benefit of running the very hot water through
all the pipe work like you would with multiple TMVs at every point of use.

In the end I went for a high flow TMV, and set it at max temperature
(about 55 IIRC). That allows for some heat loss in the pipes and still
delivers water hot enough you can mix in some cold at the point of use -
giving shower valves etc a bit more control.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd -
http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

Bob Eager[_7_] January 12th 19 01:03 PM

how hot do you run you CH boiler
 
On Sat, 12 Jan 2019 07:35:10 +0000, John Rumm wrote:

manual - adjust the flow temperature yourself in response to
particularly cold days - probably works quite well for users who are
clued up enough to understand the requirement.


This is what I do. The boiler is in the downstairs loo at the back of the
house, and I see it frequently!

--
My posts are my copyright and if @diy_forums or Home Owners' Hub
wish to copy them they can pay me £1 a message.
Use the BIG mirror service in the UK: http://www.mirrorservice.org
*lightning surge protection* - a w_tom conductor

Dave Plowman (News) January 12th 19 02:08 PM

how hot do you run you CH boiler
 
In article ,
tim... wrote:
Anyhow, at my current house it is 55 and works perfectly well


You must have rather oversized rads?

--
*Failure is not an option. It's bundled with your software.

Dave Plowman London SW
To e-mail, change noise into sound.


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