Any point installing TRVs with this boiler?

Spies

I have a Swiftflow 75/80 but looking at the manual it doesn't appear to have any intelligence with regards to turning down the flame based on the temperature of the CH hot water return.

Therefore, other than from a comfort point of view, would there be any point in installing TRVs on my radiators?

southcoastrgi

TRV's operate by reading the temp around the head & therefore control the temp of the room, they have no effect at all over what temp the rad/boiler/pipework gets to, so yes being able to automatically switch off different rooms at different temps will save money

Spies

I know how TRVs operate.

The point I am trying to get across is that the boiler doesn't have flame modulation so other than possibly increasing the flow rate of the system when radiators close, it won't save gas because the thermostat that controls the boiler is in the lounge - this is the coldest (largest) room but also where we spend most of our time.

The increased hot water return temperature from shortening the system from having some radiators closed, won't benefit me as the boiler will just fire for the same amount of time that the stat requests.

Spies

OK so looking into it more, the boiler has both CH and DHW thermistors, there is also a modulator on the control board, so this should imply that it can in fact control the intensity of the flame?

southcoastrgi

If you know how TRV's work then why are you asking the question you did ?
The fact that you aren't heating rooms un-necessarily will mean you reduce your gas usage, your room stat is just off & on so yes the boiler will continue to run until it has reached the temp you have set on the boiler stat, your boiler doesn't have a thermistor on the return anyway so I'm not sure why you think that is relevant, the boiler stat controls the temp your rads get to & TRV's the individual rads so like I said installing them will save you money by not having rads blasting away in bedrooms when you don't need them to

stator

I can't imagine a boiler that didn't cut out once the return temperature reached a certain level. Surely it would be too dangerous to keep overheating the water?

xyz123

Spies wrote: »

I know how TRVs operate.

The point I am trying to get across is that the boiler doesn't have flame modulation so other than possibly increasing the flow rate of the system when radiators close, it won't save gas because the thermostat that controls the boiler is in the lounge - this is the coldest (largest) room but also where we spend most of our time.

The increased hot water return temperature from shortening the system from having some radiators closed, won't benefit me as the boiler will just fire for the same amount of time that the stat requests.

Theoretically, if trv works and shuts off heating in one room that means all heat from boiler is diverted to other radiators. This journey means the lounge reaches the thermostat set point quickly leading to boiler shutting off....

tacpot12

Stator has provided the basis for the answer. The Swiftflow doesn't modulate its heat output by reducing the flame but by running for less time.

It does sense the temperature of the water as it returns to the boiler and will fire it is too low and there is a heat demand from the roomstat. If all the TRVs are closed it will take longer before the return temperature drops below the point at which the boiler will fire. Thus the boiler is off more of the time.

So TRVs do save money even with old boilers.

martinsurrey

tacpot12 wrote: »

If all the TRVs are closed it will take longer before the return temperature drops below the point at which the boiler will fire. Thus the boiler is off more of the time.

So TRVs do save money even with old boilers.

almost 100% correct with just one pedantic point

The water in the active part of the system (the part not shut off by TRV) will cool just as fast, but there is less volume of water to heat (a lot is locked in the TRV closed parts of the system), so the boiler will fire for a shorter time to bring it back up to temp.

same result (saved cash), but different reason.

southcoastrgi

tacpot12 wrote: »

The Swiftflow doesn't modulate its heat output by reducing the flame but by running for less time.

It does sense the temperature of the water as it returns to the boiler and will fire it is too low and there is a heat demand from the roomstat. If all the TRVs are closed it will take longer before the return temperature drops below the point at which the boiler will fire. Thus the boiler is off more of the time.

It has a modulating gas valve so it does reduce the heat output.

It only has one thermistor for the heating which is located on the flow so it doesn't sense the temperature of the return at all, the pump speed determines the differentiation between the flow & return

Hedgehog99

Having TRVs scores you some points if you're having an EPC done prior to selling or renting out your property.

(as does fitting low-energy light bulbs to every possible fixed light - just in case anyone reading this is about to get one done & didn't know)