Which thermostat has priority on heating system?

silvercar

The boiler 'listens' to its own stat first and then the room stat. So if the boiler temp is already above 80 it won't need to come on. But if it is below 80 and the hall is below 18 it will come on.

The TRVs just switch the rad they are attached to off if the temp at that rad (approx= in that room) gets too high.

slipthru

The room thermostat in the hall takes priority over the trv's in telling the boiler to stop firing. If the boiler is constantly on then try lowering the thermostat a degree or two.

I've moved my wireless thermostat into the living room and put the trv's to 4 as the hall is just to cold and if i set the thermostat to 18 i don't think the boiler would have stopped.

essexsi_2

Thanks iamcornholio and silvercar. I am now a lot more informed thanks to all of you!

Ok, the plan is to keep boiler stat at 80, hall stat at 18 and TRVs 3 downstairs, 2 upstairs. Lets see how they get on with that!

Cheers for all your help. Si

essexsi_2

slipthru, you really did while I was typing my reply!!!!

That is the trouble, as the hall is quite cold the boiler seems to have been on most of the day trying to satisfy the room stat. Like iamcornhoilio said though, is the boiler just firing to heat that one radiator if all the other radiators TRV's are satisfied and so is not too bad?!?

Cheers Si

iamcornholio

Incidentally, if the boiler is a condensing type, then you should aim to have the returning water temperature low to ensure that the boiler runs in condensing mode and therefore more efficiently.

A lot of this will depend on the radiator sizing (ie to give out more heat so as to cool the returning water), but it may not be just a case of setting the boiler to 80

Perhaps a more experienced plumber can advise

DVardysShadow

essexsi wrote: »

I still do not really understand which of the stats the boiler 'listens' to as a priority?

Priority does not come into it. This system will have different priorities in spring and autumn than it has now.

The boiler has its own 80degC thermostat and will always try to maintain that temperature. The thermostatic valves do not interact directly with the boiler. However, they regulate the flow of water in the system. So if the room temps are right, the TRVs will largely shut down, flow will be low and the boiler will not need to fire so often to maintain 80degC water temp. If the rooms are cold, the flow will be much higher and the boiler will need to fire for longer.

The one rad with no TRV and a room stat operates on top of the system already described. When it is cold - like this month, the rad, if correctly sized - ie a little bit small - will not heat up the hall, so the boiler will operate as long as the timer allows. But in autumn an spring, you can expect the rad to heat the space to temp - at which it will shut the boiler down until the room temp drops..

For comfort now, set the room stat to just above the temperature the rad can maintain and set the TRV's to desired room temp. Come spring, you will find the boiler will fire on and off for an hour or so to heat up the house and then the room stat may limit it to firing for 5 mins in 20 mins, say.

stevemcol

Lots of good answers. I'll just stick my oar back in.

The various stats don't have particular priority, they all work together.
80° for the circulating water keep the boiler working at an efficient output and not really connected to house temperature.
The hall is a good place to have your room stat. A sensible temperature in the hall will help you keep your rooms warm. A previous poster said an open front door and draught can cause the boiler to fire. That's no bad thing and serves to replace the heat in your house.
For a nominal 18/19 set in the hall, you should be able to maintain 20° or more in your main rooms.

The rad stats will have 'priority' just in the room they operate.
So as I suggested, set your hall to a reasonable temp (18-20) then control your rooms with rad stats.

jennifernil

I know it is supposedly "best practise" but I really cannot see the need or sense in having a room stat when TRVs are fitted. Yes, it turns off the pump, but then if one of the TRVs calls for heat it will not get it.

We have TRVs on all rads other than the hall, which acts as a bypass. Our system has been in place over 22 years and works how we like it to work. We have living rooms, study, and bathrooms on 3-4, bedrooms we do not heat at all.

Our house is 280 sq metres and our bill is about £750 for heating and HW.

If we had to have a room stat, we would have it in the hall, set it to MAX and carry on as before.

paulsad

Try this link...
http://www.miketheboilerman.com/thermostaticvalves.htm

stevemcol

jennifernil wrote: »

I know it is supposedly "best practise" but I really cannot see the need or sense in having a room stat when TRVs are fitted.

The idea is the room stat acts as the TRV for the last radiator in the circuit (which should have a manual valve). It prevents the boiler from firing when the overall house temperature is satisfied. If the system is designed and balanced properly the TRVs shouldn't need to demand heat when the boiler isn't fired.