adding a room thermostat to my heating system

want2bmortgage3

I currently have a condensing combi boiler supplying my radiators with heat and this is controlled by a £60 drayton programmer, where i can set the timer or just have it on or off.

in the freezing cold weather, i've left it on permanently and controlled the rooms with TRVs. this worked ok, but yesterday it warmed up a bit outside and i felt the system was running unnecesarily.. costing money.

so i thought if i connect up a room stat to the programmer and set it to say, 15 degrees, then my system will shut off above this and not run unnecesarily?

i can then leave the trv's on the highest setting so it doesnt interfere with the stat? do u think this would solve my probs?

latecomer

But if you have TRVs on all radiators and they reached the desired temperature they should cut off and the boiler will not run until the water temp drops so it shouldn't be that costly?

EliteHeat

latecomer wrote: »

But if you have TRVs on all radiators and they reached the desired temperature they should cut off and the boiler will not run until the water temp drops so it shouldn't be that costly?

This is wrong. The TRVs shutting down have no impact on the boiler at all. It will continue to fire and circulate water around the underlying pipework, burning gas and costing money yet producing no useable heat.

This is why a room thermostat saves a great deal if money as is prevents the boiler from firing when not required.

A programmable room thermostat is the best option and a wireless one enables you to easily position it wherever you want without having to redecorate etc.

want2bmortgage3

Incisor - the timer is pretty useless to me really... because - I want to keep the flat from dropping too low in temperature whether i'm in, in bed, or out. The flat has had problems with condensation causing damp and mould in the past and I want to avoid that even if it means running heating when i'm out!

Elite.... thanks for clearing up the TRV thing - I though as much - as the boiler kept working even though the trvs had shut off. Elite - can you recommend a product to work alongside my drayton mk4 programmer or to replace it? Screwfix preferably as I have a voucher. Also if you could advise on fitting that would be much appreciated.

EliteHeat

This is a good one
Not such a good one, but still expensive

Neither of these need, or benefit from, any external programmer or clock.

latecomer

Eliteheat - could you clarify the boiler not shutting off behaviour. I thought boilers checked the water temperature so that it was only heating it when required otherwise it would be firing/running all the time they are on which is obviously not the case.

Hence the logic being that if the TRVs are all shut off then the heat loss would be far less than if the radiators were passing water and hence the gas comsumption would be lower due to the reduced time that the boiler is firing?

EliteHeat

latecomer wrote: »

Eliteheat - could you clarify the boiler not shutting off behaviour. I thought boilers checked the water temperature so that it was only heating it when required otherwise it would be firing/running all the time they are on which is obviously not the case.

Hence the logic being that if the TRVs are all shut off then the heat loss would be far less than if the radiators were passing water and hence the gas comsumption would be lower due to the reduced time that the boiler is firing?

I'm only too happy to.

Current building regulations (part "L", energy efficiency) call for, amongst other things, that an interlock be provided on all new or replacement heating systems.

An interlock is simply an arrangement of controls that positively start or stop a boiler in reponse to a central demand for heat. For instance an interlock could comprise of a timeswitch and a seperate room thermostat or more simply a programmable room thermostat. The interlock requirement would not be met by just providing a programmer or a timswitch since these devices have no capability to measure the temperature and therefore do not properly 'demand' heat - they simply turn the boiler on or off.

The regs also state that the room space measured by a wall thermostat should not contain a radiator fitted with a TRV. The reason for this is that a user could turn the TRV down, thus preventing the required temperature from ever being met and therefore nullifying the interlock completely.

The purpose of TRVs is to provide localised temperature control and they simply vary the heat being allowed to pass through a radiator depending on the ambient temperature being sensed by the TRV.

In theory, if evey radiator in a property has a TRV fitted and they are all shut, then water could only circulate around the underlying pipework. There is a technical reason why this is unlikely to happen but I won't go into this.

The point is that this is not useable heat which does incur a cost in terms of gas used. As you point out, the boiler will sense the water temperature and shut down its main burner, depending on the setting of its thermostat, but the pump will continue to circulate water uselessly around the system until the system water temperature has dropped sufficiently to allow the boiler to re-fire.

Depending on the quality of the installation, the heat loss under these circumstances could be negligible (unlikely) or significant (more likely). However, as boiler efficiency now appears to be measured to a least one decimal place, the government has decided that this useless cycling is unacceptable.

That is why installers fit room thermostats.

EliteHeat

andrew-b wrote: »

Personally i like to keep things simple which is why i opted for a basic wired mechanical thermostat over a wireless one which i was offered with my boiler change..much less obtrusive too. We have this one
...considerably cheaper so your initial investment will be clawed back in no time by the savings in energy.

For what it is worth ......

The OP has a combi boiler and so the stat in your link would be unsuitable as it is designed to have live and neutral connections and switches 230V. This would almost certainly destroy the boilers PCB.

In addition, it is unlikely that he has any wiring in place for a wired stat. Although, if he has been converted for combi operation then he might originally have had a room stat but the wiring would probably terminate in an unsuitable place - unsually the airing cupboard.

want2bmortgage3

it depends where the best place is for the thermostat.. my lounge is at the front of the property with kitchen next to it also on the front. as you go in the kitchen the boiler is on the left, on the front wall under worktop height. the current programmer is on the wall between the kitchen and lounge. so i think it could be possible to put a stat in the lounge on the other side of the wall from the programmer.

a wireless one is quite appealing though as it could be moved if necessary and i guess it can be stuck to the wall instead of drilled?

vaio

EliteHeat wrote: »

……….In theory, if evey radiator in a property has a TRV fitted and they are all shut, then water could only circulate around the underlying pipework. There is a technical reason why this is unlikely to happen but I won't go into this.

The point is that this is not useable heat which does incur a cost in terms of gas used. As you point out, the boiler will sense the water temperature and shut down its main burner, depending on the setting of its thermostat, but the pump will continue to circulate water uselessly around the system until the system water temperature has dropped sufficiently to allow the boiler to re-fire.

Depending on the quality of the installation, the heat loss under these circumstances could be negligible (unlikely) or significant (more likely). However, as boiler efficiency now appears to be measured to a least one decimal place, the government has decided that this useless cycling is unacceptable.

That is why installers fit room thermostats.

I thought rads were normally fitted in parallel so if they all have shut TRVs then there is no flow.

Last time I was involved with a combi (back in the early 80’s) we had to fit a by-pass which was always open. If the boiler only saw the flow due to the by-pass it wouldn’t fire, if one of the TRVs opened then the boiler would see the flow due to the open TRV and the by-pass and would fire.

EliteHeat

vaio wrote: »

I thought rads were normally fitted in parallel so if they all have shut TRVs then there is no flow.

Last time I was involved with a combi (back in the early 80’s) we had to fit a by-pass which was always open. If the boiler only saw the flow due to the by-pass it wouldn’t fire, if one of the TRVs opened then the boiler would see the flow due to the open TRV and the by-pass and would fire.

The boiler 'sees' nothing and if a combi or a system boiler it will have an internal bypass. The part I specifically did not mention was that if all rads are shut and there is no bypass at the end of the circuit, then there can be no circulation at all (depending on how the system was piped up) - except via the internal bypass. This is probably at a level beyond the scope of this thread though