How to optimise your combi boiler

Our heating system is new(ish) and when I spec'd it - I did so using delta T50. Our flow temperature is nice and low. Problem is, unless the radiators are sized to suit the lower temperature.. the rooms are going to get cold.
 
If you have weather compensation or load compensation installed moving the dial on a combi boiler wont work as its already optimized to be the most efficient it can be.
 
Skilid said:
Should change the title to "combi boiler". You cann't lower flow temps on a standard boiler otherwise you won't heat your hot water properly.
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I didn't realise it was combi boiler only. You can lower the flow temperature though. But the minimum tepmerature is 60C.

GeX said:
Our heating system is new(ish) and when I spec'd it - I did so using delta T50. Our flow temperature is nice and low. Problem is, unless the radiators are sized to suit the lower temperature.. the rooms are going to get cold.
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Wow, how are you achieving a 50C dT? I believe having a lower flow temperature with longer running hours is more efficient. Particularly if you have a condensing boiler that condenses because you have a low return temperature.
 
My Ideal 35 boiler has a temp dial which as an "E" setting on it for the CH so it's set to that. I'd like to think this is the most efficient setting.

I believe it also has weather compensation as there is a little white box on the outside wall behind the boiler with wires going back into the house. Would that be right?
 
dirtychinchilla said:
Wow, how are you achieving a 50C dT? I believe having a lower flow temperature with longer running hours is more efficient. Particularly if you have a condensing boiler that condenses because you have a low return temperature.
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Boiler supports OpenTherm, and we use a Nest thermostat. This lets the thermostat request low boiler output if the temperature change is only small, rather than going full beans and waiting for the boiler to (over)heat all the rads and check the return temperature before throttling down.

Overshoots are rare, the house remains stable temperature wise and it also means the rads are never too hot for our kids to touch.
 
radio 4 .. and did you hear what a crap job the two sets of female plumbers - one from the memorable (female) stopcock company made at explaining the process,
or functioning of a condensing boiler.
.. they lost my business.
 
Richie said:
My Ideal 35 boiler has a temp dial which as an "E" setting on it for the CH so it's set to that. I'd like to think this is the most efficient setting.

I believe it also has weather compensation as there is a little white box on the outside wall behind the boiler with wires going back into the house. Would that be right?
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Nice! That definitely sounds like weather comp.

GeX said:
Boiler supports OpenTherm, and we use a Nest thermostat. This lets the thermostat request low boiler output if the temperature change is only small, rather than going full beans and waiting for the boiler to (over)heat all the rads and check the return temperature before throttling down.

Overshoots are rare, the house remains stable temperature wise and it also means the rads are never too hot for our kids to touch.
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Nice, that's very cool. I would like to have something a bit smarter in my house. At work we sell radiator valves that are self-balancing and on which you can define a flow rate, which would improve things massively. But they're about £200 to kit my house out and I can't afford that atm.

I'm also very keen on getting weather comp. That's expensive too. OpenTherm invalidates the warranty on a Vaillant boiler apparently.
 
GeX said:
Our heating system is new(ish) and when I spec'd it - I did so using delta T50. Our flow temperature is nice and low. Problem is, unless the radiators are sized to suit the lower temperature.. the rooms are going to get cold.
Click to expand...
I did the same, though to T35, bigger rads cost almost no extra so it made sense, I basically increased rad size by 150% over what they would normally be sized at.
Opentherm same as you as well and full per room controls so over winter I'll just be heating the living room a lot of the time with nice cool flow temperatures of usually around 25c.
 
robj20 said:
I did the same, though to T35, bigger rads cost almost no extra so it made sense, I basically increased rad size by 150% over what they would normally be sized at.
Opentherm same as you as well and full per room controls so over winter I'll just be heating the living room a lot of the time with nice cool flow temperatures of usually around 25c.
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I remember you helping me at the time, and I've just gone back and double checked the sizing I used and it is actually based on T30 rather than T50 as I'd remembered. I have it all in a big spreadsheet, and the calculated BTU needed for out lounge is around 4500 but the radiator in there is 9500 at T50, and around 4900 at T30.. and in the installation notes I've got "delta T30 BTU ratings" :D I think I even used the plumbers you recommended to install it all (https://www.mycentralheating.co.uk/) ?

I never went as far individual room control, other than TRVs.
 
robj20 said:
I did the same, though to T35, bigger rads cost almost no extra so it made sense, I basically increased rad size by 150% over what they would normally be sized at.
Opentherm same as you as well and full per room controls so over winter I'll just be heating the living room a lot of the time with nice cool flow temperatures of usually around 25c.
Click to expand...

So, bigger rads with lower temp equals cheaper bills and warm rooms?
 
optimum temperature with the condensing boiler and big rads is 45 outgoing not 25 ? and then hoping for a 20C @return.

with a combi boiler(no tank) it is the water heating duties that demand a high Kw boiler - mines 30 but I'd hope it is only using <5 to heat the house on a <5C day
and 5 * 5p/gas/kwh* 12 hours a day would be £3/day.
 
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