# Thermostat Confusion

#### Alex Alnwick

I live in a relatively new house.

Gas boiler serving radiators in all rooms.

Lounge has 2 radiators controlled by thermostat on the wall

Hall / landing has single radiator in each with thermostat in the hall

All other rooms have single radiator with thermostatic valve.

We set the thermostat in the lounge to 20C, hall is 18C

We were told by the builder's heating contractor that in this configuration, the hall thermostat controls the heat in the upstairs of the house and the kitchen and dining room.

If that is the case, what is the point of thermostats on each radiator, as changing them to max will not increase the temperature above 18C? Or am I missing something?

Regards

Alex

The individual TRVs on each room will allow you to select a relative hotter or colder room when the heating for that zone is on; it's not a gradual selection the valve is either fully open or closed, the numbers just thermostatically indicate when it will close.

But yes you are right, if for some reason the hall reaches the selected temperature before your upstairs actually feels warm then the TRVs won't be doing much as the zone won't be requesting heat anymore, despite the TRV being open.

But usually, the hall is the coldest spot so it should work out, since the plan would be that the TRV reach temperature and close before the hall thermostat does and when set to "5" or something in the TRV this should more than 18C in the room.

OK. I think I'll experiment a bit and see what happens - it just seems a strange way of control to me.

As the hall is the coldest room, generally, to have it set the maximum for the upstairs rooms makes no sense to me.

In order to put more heat upstairs, I have to heat the coldest and most underused room in the house?

OK. I think I'll experiment a bit and see what happens - it just seems a strange way of control to me.

Whilst experimenting, checking if either of the two thermostats can in fact trigger the boiler as it does seem an odd arrangement. Turn both to minimum, let the house cool down, then wack one stat to max. wait to see if the boiler lights up, then return stat to min. Then repeat the process with the other stat.

There should be no TRV's fitted to the two radiators in the living room, nor the rad in the hall.

Yes it does sound like an unusual layout.

Normally a thermostat upstairs would control the upstairs loop and a thermostat downstairs control the downstairs loop.

There should be no TRV's fitted to the two radiators in the living room, nor the rad in the hall.

That's as it is.

As a minor experiment I set one of the TRVs in an en-suite to 5. The thermostat in the hall is set to 18C and the temperature at the moment is 18C.

Opening the en-suite TRV had no effect at all - the radiator was still cold after 30 mins

As the hall is the coldest room, generally, to have it set the maximum for the upstairs rooms makes no sense to me.

That doesn't sound as if it is in the coldest room. The idea is, as you say, that the thermostat is located in the coldest room (i.e. the last one to warm up) so that all of the other rooms on the same heating circuit warm up first, but aren't overheated because their TRV's stop that happening. Then heating continues to run for a bit longer to heat up the cooler area where the room thermostat is located before switching the thermostat off.

Building regulations require this arrangement as a boiler interlock to save energy. The TRV's only regulate the radiators in the rooms they are located. The thermostat provides the boiler interlock that shuts the heating down when everywhere is warm.

I had a similar arrangement and it didn't work too well initially, so I downsized the hall radiator so that the hall took longer to heat up than the other rooms and all was well after that.

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