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  #41   Report Post  
Old January 12th 19, 01:13 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 09:28, wrote:
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.* 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)


The combi won't usually get it any hotter (since flow rate and
temperature are mutually exclusive), but the again there is no
significant store of water to act as a breeding ground either.


--
Cheers,

John.

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

  #42   Report Post  
Old January 12th 19, 01:18 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

John Rumm was thinking very hard :
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.


I just have one TMV, on a toilet wash basin. I put that in so kids
could use the single tap I installed, to wash their hands
un-supervised, with no risk of too hot water.
  #43   Report Post  
Old January 12th 19, 01:27 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler



"[email protected]" wrote in message
...
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?


in the hall way

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.


works OK in my current house which is, presumably, balanced properly

tim



  #44   Report Post  
Old January 12th 19, 01:31 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 08:38, Harry Bloomfield wrote:
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.


Many CH installers would probably argue that is the case... but it can
make a system less nice to live with. Especially if you have rooms that
don't get adequate flow until nearly all the other rads have throttled
on their TRVs, or worse, never get to set temp because the main stat has
turned the whole system off.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
  #45   Report Post  
Old January 12th 19, 01:31 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler



"Dave Plowman (News)" wrote in message
...
In article ,
tim... wrote:
Anyhow, at my current house it is 55 and works perfectly well


You must have rather oversized rads?


Nope

they are tiny

they are on all day

The house is well insulated

Why do you think that wouldn't work?

tim



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

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




  #46   Report Post  
Old January 12th 19, 01:32 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler



"John Rumm" wrote in message
o.uk...
On 12/01/2019 09:28, wrote:
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. 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)


The combi won't usually get it any hotter (since flow rate and temperature
are mutually exclusive), but the again there is no significant store of
water to act as a breeding ground either.


the linked to article said that the water in a shower head was sufficient

tim



  #47   Report Post  
Old January 12th 19, 01:36 PM posted to uk.d-i-y
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Posts: 22,508
Default how hot do you run you CH boiler

On 12/01/2019 10:25, RJH wrote:
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.


Probably no more sensors, than any other zoned system (i.e. one for each
stat, plus the external one), but the fact that it can read actual
temperatures from each does open up some more possibilities.

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'.


You could do, although a pair of two port valves is the more common way
of doing it. It does depends a bit on how the pipework is done. Some
systems are easy (say where pipework for each floor of rads is run under
the respective floor), and some very difficult (say where all the
pipework is under the upstairs floor, and then branches both up and down
to feed rads).
A single switch would be easier than faffing about with 4 TRVs each
evening.


Indeed - or even a timer / programmable stat for each floor.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
  #48   Report Post  
Old January 12th 19, 01:44 PM posted to uk.d-i-y
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Default how hot do you run you CH boiler

On 12/01/2019 00:59, RJH wrote:
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.


That was my 'understanding', but not what was stated in the admittedly
dumbed down instructions, which talked about the startup procedure as
"lighting the boiler", as if it has a pilot light rather than igniting
the gas as required.

--
Max Demian
  #49   Report Post  
Old January 12th 19, 01:46 PM posted to uk.d-i-y
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Posts: 38,253
Default how hot do you run you CH boiler

In article ,
tim... wrote:


"Dave Plowman (News)" wrote in message
...
In article ,
tim... wrote:
Anyhow, at my current house it is 55 and works perfectly well


You must have rather oversized rads?


Nope


they are tiny


The physical size depends on the demand in that area.

they are on all day


The house is well insulated



Why do you think that wouldn't work?


Anything can work. But there is an ideal figure for rad temp for best
efficiency.

--
*If you lived in your car, you'd be home by now *

Dave Plowman London SW
To e-mail, change noise into sound.
  #50   Report Post  
Old January 12th 19, 01:54 PM posted to uk.d-i-y
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Posts: 1,739
Default how hot do you run you CH boiler

On 12/01/2019 10:19, RJH wrote:
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 downloaded the manual and it omits the critical "or below".

--
Max Demian


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