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. Twat
Anyhow, at my current house it is 55 and works perfectly well
what do you guys/galls do
tim
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On 11/01/2019 18:52, tim... wrote:

Indeed...

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

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

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.
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On 11/01/2019 21:30, John Rumm 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.
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That may be true, but in practice I don’t think Legionella has ever proved to be a problem in domestic systems.
Tim
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On Friday, 11 January 2019 22:35:12 UTC, Tim+ wrote:

er proved

Oh yes it has. Plenty of people have died. https://www.dailymail.co.uk/news/article-4569428/Deadly-Legionnaires-bug-lu rking-1-5m-British-homes.html
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On 11/01/2019 21:30, John Rumm wrote:

snip

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?
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On 12/01/2019 00:55, RJH wrote:

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/File:VaillantVRC470HeatingCurve1.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/File:VaillantVRC470HeatingCurve2.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.
--
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John.
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John Rumm pretended :

Balanced?
I have always assumed there was no need to balance a system, where TRV's are installed.
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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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On 12/01/2019 09:10, tim... wrote:

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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on 12/01/2019, dennis@home supposed :

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.

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

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.
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in the hall way

works OK in my current house which is, presumably, balanced properly
tim
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On 12/01/2019 08:38, Harry Bloomfield wrote:

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.
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On Saturday, 12 January 2019 13:31:13 UTC, John Rumm wrote:

IMLE it's essential to balance the system with TRVs set to max temp before using the TRVs to improve balancing as needs change.
NT
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On 12/01/2019 07:30, John Rumm wrote:

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

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

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.

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).

Indeed - or even a timer / programmable stat for each floor.
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On 12/01/2019 10:25, RJH wrote:

If the pipework is in the right place a two port valve will isolate the upstairs.

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

Look at the Honeywell Evohome system www.heatingcontrols.honeywellhome.com/products/Underfloor-Heating/evohome-Main/
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The site exists, but not with the www.
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On 13/01/2019 15:51, Graham. wrote:

I had a quick look, thanks, but that's overkill for me. And thanks to the others regarding isolating/regulating.
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