Combi heating query

[mikej100]

A friend had a new Gloworm combi boiler fitted 6 weeks ago but says that when the heating comes up to temp and cuts out it is not until the room in which the room stat is in becomes quite cool before the heating cuts back in again.
He has set the stat at 18deg and the rad in this room has a TRV set to max.He has replaced the room stat to eliminate this but is there any other adjustment or possible cause.
Have read about return temp adjustment anybody explain this.
Any ideas or suggestions appricated.
Thanks Mike.

 

[andrew1210]

18 deg. c. can seem quite cool compared to the likes of 21/22 deg. c.. He could try placing a thermometer next to the thermostat to check it is operating properly by checking the temperature when the heating is firing. Has the thermostat been placed near a heat source?

 

[plumbnuts]

The room containing the stat should not have any TRV's fitted.

 

[mikej100]

what is the reason for not having a TRV near the stat?

 

[andrew1210]

Having a trv near the stat defeats the purpose of the room stat in a way as it gives another degree of control over the temperature of the room, which can interfere with the room stat,

 

[mario500]

Think about it..... Trv shuts down - room cools - room stat senses change and heats the rest of the house more than is required.

This general rule of thumb is part of basic practise building regulation.
The room where the room stat is located should have a radiator with wheelhead and lockshield valves only.

 

[mikej100]

I can see your point guys but the TRV is set to max and it is this room that appears cold before the heating fires.
Apart from removing the TRV whats the best setting for both the stat and TRV that we should use to get best performance with what we've got?

 

[Happyplumber]

mario is totally correct ,there is absolutley no point in having a TRV and thermostat in the same room,they will be fighting each other and not true reflection of how the house is heating up

for temporary measure until you can change it over to a normal rad valve unscrew the head and see how you get on

 

[mikej100]

Thanks alot guys great advise and if we remove the TRV and still have the same is there likely to be any other adjustments that we could look at or is that it?

 

[mario500]

You may have an issue with the boiler itself.

If the room stat is calling for heat, but the boiler is cooling too much before it fires back up, then you might need to get it checked.

I have had similar problems with Glowworm boilers before.

Maybe check the pump is working properly???

You need to get the flow and return temps checked and how quickly the boiler fires (ie temps)

Hope that is of some use

Allan