Radiators are getting very hot when thermostats are all low

22 Oct 2014
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United Kingdom
Hi all

I have all my TRV's set to number 3 which I believe is average, I have my room stat set to 18 degrees, and my boiler stat set at 4 o'clock (12 - 12). Can anyone suggest why my radiators intermittently seem to be belting out heat (like almost too hot to touch), when the stats are all low ?

Could drafts be a factor with this ? It was very windy yesterday and I know our house is not that well insulated.

I want to be sure that there isn't a fault with the system, because our energy bills are high, and I'm thinking it could be related.

I appreciate any help.

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The TRV is a thermostat not a simple restricting valve so they can allow radiators to get hot if they are cool, to my understanding there are two types of valve, the older valve needed to be fitted correct way around and tended to switch on/off not gradually open close, the latter valve gradually opens and closes and can be fitted either way around, there are also different heads used on the valves varying from wax to electronic. Depending on head type is the range they work in, most non electronic have about a 3°C range between fully open and fully closed, mainly because the heat from the radiator will affect the setting, the electronic heads use two sensors and the air temperature is corrected by water temperature so work within a degree of setting. However the electronic also has anti hysteresis software built in so which means they are to my mind slow to respond to setting changes.

And of course any wall thermostat can completely mess up TRV operation unless linked with something like IFTTT I found my wall thermostat was set too low for the TRV to work correctly it was also set to 18°C in the hall, but with doors left open it would switch off before rooms were warm enough, I would hear the motors in my electronic heads running again and again as it opened the valve more and more, then the thermostat would close and the valves would then heard again and again closing, just one peg up on the wall thermostat stop and it seemed to settle down, had the same been happening with non electronic you would not know as no sound.

I think my old expensive thermostat which has anti hysteresis built in is not the best option when the valve heads also have anti hysteresis built in they seem to fight each other, I suppose today we should not need wall thermostats? however EvoHome is expensive so as yet I just trim the settings as best as I can, and it's not that bad.

You could use fan assisted radiators where the fan speed varies according to room temperature which in theory is the bees knees, because air is circulated whole room at same temperature, however although the return water temperature will control boiler flame height I can see how the boiler is switched on/off other than manually so it seems there is no perfect system?
Makers numbers and temperatures vary but lets say that no. 3 on trv is 20 degrees. Room temperature is15 degrees, valve will be wide open therefore rad will come up to whatever temp boiler stat is set at. As room temperature increases, valve will begin to close and rad will become tepid and eventually if 20 degrees is achieved valve will be completely closed. Valve may be wide open at 18 degrees and partially open at 19 degrees.
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How does all that help the OP solve his problem?
Completely agree so much drivel, unless you have a thermal store just turn down the boiler thermostat, will solve your problem and save you money on your gas bill.

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