Discuss Advice on Flow and Thermastat in the Central Heating Forum area at PlumbersForums.net

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I live in a very cold 3 bed detacthed house. We have a Baxi 400 heat only boiler and use Tado smart thermostat and controler to replace the old honeywell programmer. Pump is a CirculatingPumps CP50. The boiler flow temp is set at 75c and the thermistat is at 21c but it is not warm enough and making the bills higer and the boiler is on quite a lot.
My question is would it be better to increase the Flow Temp to 80-85 (it goes to 90c) or icrease thermistat more. Whatever saves cost.
 
What is your Tado thermostat saying is the actual temperature in the room (not the set temperature)?
If the room actually reaches 21, then it's the thermostat that is limiting heating. It seems that temp. is not warm enough for you, so turn the thermostat up.
If the temperature of the room is not reaching 21, you need more heat out of the system.
There are probably various ways of achieving that - I leave the experts to advise. I don't think just turning up the boiler temp is going to be the full answer, and may be less efficient.
whatever you do to increase the heat in your house, likely more energy consumed will use more fuel, so will increase cost.
 
The Tado thermastat say room temperature is at 21c (which it is using a manual thermometer) but if I turn the thermistat to 22 or above up the Boiler very rarely sitches off as temp does not get that high.
That is what made me think if i turned flo temp up it would make radiators hotter so reaching temp.
Basicall i dont want to do that if it is putting cost up to a very large amount. And someone told me those boilers are not designed to be that high.
Also wondering what is the optimal flo temp of that boiler.
 
I'm hoping professionals will be along to advise, but I thought the generic optimal temp. range for condensing boilers was between 60 and 70 deg.
Have you tried doing rough heat loss calculations using an online tool, to check if your radiators are properly sized for your rooms?
 
If the radiators are all hot then it is probably due to draughts or poor insulation.

When you checked the tad sizing did you allow for the correct R value of the insulation and correct ΔT for the radiators?
A boiler, particularly a condensing one, becomes less efficicient the higher the flow temperature is set.
 
Hi RikkiDees,

Firstly let me state that I am NOT a plumber.
We also have a Heat Only Boiler - for reference only an Ideal Logic Heat H15, paired with Drayton Wiser Thermostats.

When a Heat Only system was installed (prior to 2023) then the designed flow and return temps would typically be 80'C Flow, 60'C Return giving a 20'C differential.

This is BAD as condensing boilers only start condensing when the return temp is 54'C or lower. The lower the Return temperature the more efficient your boiler will be to a maximum of around 94%.

Approximately:
80/60'C - 80% efficient
74/54'C - 85% efficient
64/44'C - 94% efficient

So turning up your Flow Temperature will increase your gas use and decrease your efficiency (meaning you use more gas).

1) Is your boiler running efficiently?
When was it last serviced? There are seals and electrodes that can deterioate that adversely affect your boiler performance.
2) Is your system dirty/blocked
A dirty system (sludge) will impede flow and reduce the heating output of your radiators.
3) Is your system balanced?
Our house is only a few years old but the system was not balanced correctly. This means adjusting the flow through the radiators so that the liquid doesn't skip radiators.
4) I guess it is possible that the Flow Sensor is faulty (but I would expect you to have other issues, eg Hot Water would be too cold or too hot)
5) Can you fit OpenTherm Controls (Nest in OT Mode/ EPH and a few others).
Whenever possible you should fit OpenTherm controls (or the manufacturers equivalent standard).

*) I looked through the manual for the Baxi 400 Heat Only Boiler and unfortunately it doesn't appear your boiler has OT Controls and the Baxi Usense Smart room thermostat only works with Baxi Combi Boilers.

**) You can also purchase "Auto Balancing TRV's" and "Auto Balancing Valves"

I hope that helps in some way
 
If the radiators are all hot then it is probably due to draughts or poor insulation.

When you checked the tad sizing did you allow for the correct R value of the insulation and correct ΔT for the radiators?
A boiler, particularly a condensing one, becomes less efficicient the higher the flow temperature is set.
Hi yes I believe so I got a friend who did his check to do mine. He had his confirmed by a heating engineer so I am taking it on face value he knows what he is doing. Although I try to lower the flow it just does not get to temp. Put it higher the rads get really hot and just make the room temp of 21c
 
Hi RikkiDees,

Firstly let me state that I am NOT a plumber.
We also have a Heat Only Boiler - for reference only an Ideal Logic Heat H15, paired with Drayton Wiser Thermostats.

When a Heat Only system was installed (prior to 2023) then the designed flow and return temps would typically be 80'C Flow, 60'C Return giving a 20'C differential.

This is BAD as condensing boilers only start condensing when the return temp is 54'C or lower. The lower the Return temperature the more efficient your boiler will be to a maximum of around 94%.

Approximately:
80/60'C - 80% efficient
74/54'C - 85% efficient
64/44'C - 94% efficient

So turning up your Flow Temperature will increase your gas use and decrease your efficiency (meaning you use more gas).

1) Is your boiler running efficiently?
When was it last serviced? There are seals and electrodes that can deterioate that adversely affect your boiler performance.
2) Is your system dirty/blocked
A dirty system (sludge) will impede flow and reduce the heating output of your radiators.
3) Is your system balanced?
Our house is only a few years old but the system was not balanced correctly. This means adjusting the flow through the radiators so that the liquid doesn't skip radiators.
4) I guess it is possible that the Flow Sensor is faulty (but I would expect you to have other issues, eg Hot Water would be too cold or too hot)
5) Can you fit OpenTherm Controls (Nest in OT Mode/ EPH and a few others).
Whenever possible you should fit OpenTherm controls (or the manufacturers equivalent standard).

*) I looked through the manual for the Baxi 400 Heat Only Boiler and unfortunately it doesn't appear your boiler has OT Controls and the Baxi Usense Smart room thermostat only works with Baxi Combi Boilers.

**) You can also purchase "Auto Balancing TRV's" and "Auto Balancing Valves"

I hope that helps in some way
Hi yes it does help.
The flow temp to 80c and it just makes it to the room temp of 21c but the boiler is on an off all the time like the water is cooling to quick and then thermostat kicks in again.
I am going to try tomorrow to leave it on all day at a flow temp of 65 - 70c and see if having it on continuously 24 hours will help. But no good if energy cost is going to go through the roof.
 
The flow temp to 80c and it just makes it to the room temp of 21c but the boiler is on an off all the time like the water is cooling to quick and then thermostat kicks in again.
If the boiler is cycling on and off while room temperature is below the thermostat set-point ('target') you probably have insufficient circulation. This might be a faulty pump, pipework and/or boiler heat exchanger blocked with sludge, etc.

Oversized radiators and 80°C flow, with proper circulation your house would be feeling not just warm but tropical.

P.S. I can't read all of the posts because they are being covered with huge adverts. @Dan, are you there?
 
What’s the room temp when the boiler is set at 65 ignore the tado
 
At 65 the room temp gets no higher than 17.5c and boiler does not go off when its trying to heat the tank

What about heating (room) only I’m guessing that test was heating and hot water on together?
 
If the boiler is cycling on and off while room temperature is below the thermostat set-point ('target') you probably have insufficient circulation. This might be a faulty pump, pipework and/or boiler heat exchanger blocked with sludge, etc.

Oversized radiators and 80°C flow, with proper circulation your house would be feeling not just warm but tropical.

P.S. I can't read all of the posts because they are being covered with huge adverts. @Dan, are you there?
Well yes I would of expected it to be too hot. The pump is just over two years old and so is the boiler (Just over 2 years)
 
No at 65c with the water on its own the boiler just keeps going until the end of the timer session which is set at 1 hour & 40 mins

What cylinder do you have and any pictures of it ?
 
Yes the bypass is fine tbh can be shut as you have a 3 port
 

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