Room Thermostat

[RickO]

What is the best room thermostat to use with a radiator system? I have tried a few electronic ones and have always returned to a Honeywell mechanical type with accelerator as it seems to be the best at maintaining an even temperature. Where is fails is in the spring and autumn when heating is needed only a little and the resistor needs to be heated up so the heat comes on and goes off without the radiators getting hot.
My system is fairly slow and the boiler never goes off on its thermostat (Roger Bisby advice many years ago) as the rads are a bit oversized; The boiler is a Glow-worm condensing.

Thanks in advance

[Roger_Bisby]

Hi Rick

The mechanical thermostat is still a good bet in many ways since the shunt (anticipator) prevents cycling of the boiler. The fact that the radiators don't get hot in the spring and autumn is a bit baffling because the thermostat should switch the boiler on and run it up to heat so the room stat becomes satisfied. It sounds as if the shunt is cutting it off on its own. This could be the wiring or a faulty stat.

If the job will stand the cost I now mostly fit programable stats because you can work through a range of temperatures to suit different times of the day. In the morning for example in our house we hardly need the ground floor heat above 16 deg cent except at weekends. We can also set the temperature low around 5pm and run it up a bit higher at 7pm and then start to run it down around 10pm.
The other thing I favour which may not have been around when I spoke to you on (LBC Radio?) was the weather compensator which checks the outside temperature and learns the heat up time of the building at various temperatures so it can advance and delay the switch on times. I also now fit TRVs in most rooms.
All these controls are fine if people use them but often I find people have the stats turned up high regardless of the weather.

I hope this helps.

Roger

[RickO]

Hello Roger,
I never spoke to you on LBC but I did listen often when I was changing my heating system in the early 90s.
I think I didn't make myself clear. What I meant to say is that if the temperature is very close to the desired temp the boiler comes on for a short time to heat up the resistor and the radiators do get a bit warm but they really didn't need to come on at all. I have looked at the programmable stats but my house is very well insulated and slow to change so I don't think they would be an advantage. At this cold time the house only drops from 20 to 17 degrees over night - 11pm to 6.30am. Correct me if I am wrong (any particular make?). I do have TVRs in any room that will heat up by the sun or any other heat source.
Many thanks for your reply. I
Rick

[RickO]

Hello Roger,
I never spoke to you on LBC but I did listen often when I was changing my heating system in the early 90s.
I think I didn't make myself clear. What I meant to say is that if the temperature is very close to the desired temp the boiler comes on for a short time to heat up the resistor and the radiators do get a bit warm but they really didn't need to come on at all. I have looked at the programmable stats but my house is very well insulated and slow to change so I don't think they would be an advantage. At this cold time the house only drops from 20 to 17 degrees over night - 11pm to 6.30am. Correct me if I am wrong (any particular make?). I do have TVRs in any room that will heat up by the sun or any other heat source.
Many thanks for your reply.
Rick

[Roger_Bisby]

Hi Rick

I think I see what you are saying now.

The shunt anticipator cuts in before the rads have done their job because the room is nearly at temperature anyway. If you are saying that you would prefer the rads not to come on at all in these situations then you need a thermostat with a wider band setting or perhaps just need to turn it down. Most people are looking for precise temperature control and general purpose stats therefore don't allow you to set the band wider ie. wait until the room drops to 16 deg. and then heat it up to 20 deg to give the boiler a better on off period. I wonder if setting the room stat slightly lower and disconnecting the neutral would achieve this. To be honest I have never measured the performance without the shunt.



Roger

[RickO]

Thanks again Roger,
I think I'll stick with the mechanical Honeywell as it works well most of the time.
I have tried it without the shunt and it widens the difference between on and off to an unacceptable amount.
If I find any thing better I will post it on this site.
Regards,
Rick