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Old January 11th 19, 07:52 PM posted to uk.d-i-y
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Default 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












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Old January 11th 19, 08:08 PM posted to uk.d-i-y
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Default 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.* 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


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.


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Old January 11th 19, 10:30 PM posted to uk.d-i-y
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Default 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.* 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.


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
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Old January 11th 19, 11:25 PM posted to uk.d-i-y
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Default 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.* 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.
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Old January 11th 19, 11:35 PM posted to uk.d-i-y
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Default 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 don’t think Legionella has ever proved
to be a problem in domestic systems.

Tim



--
Please don't feed the trolls


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Old January 11th 19, 11:42 PM posted to uk.d-i-y
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Default 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
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Old January 12th 19, 12:33 AM posted to uk.d-i-y
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Default 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
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Old January 12th 19, 12:48 AM posted to uk.d-i-y
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Posts: 6,417
Default 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.
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Old January 12th 19, 01:55 AM posted to uk.d-i-y
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Default 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
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Old January 12th 19, 01:59 AM posted to uk.d-i-y
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Posts: 1,614
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.


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


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