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Old January 12th 19, 08:56 AM posted to uk.d-i-y
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Default 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




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Old January 12th 19, 09:03 AM posted to uk.d-i-y
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Default 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



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Old January 12th 19, 09:06 AM posted to uk.d-i-y
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Default 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



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Old January 12th 19, 09:09 AM posted to uk.d-i-y
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Default 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.
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Old January 12th 19, 09:10 AM posted to uk.d-i-y
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Default 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





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Old January 12th 19, 09:28 AM posted to uk.d-i-y
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Default 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.* 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)
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Old January 12th 19, 09:28 AM posted to uk.d-i-y
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Default 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.
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Old January 12th 19, 10:03 AM posted to uk.d-i-y
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Default 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.* 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.


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Old January 12th 19, 10:04 AM posted to uk.d-i-y
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Default 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.
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Old January 12th 19, 10:19 AM posted to uk.d-i-y
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Default 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


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