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Controlling Central Heating With eTRV and Programmable Thermostat

Postby ericmark » Mon Jun 12, 2017 11:11 am

My house is open plan, we have an old boiler, and TRV's fitted upstairs only, downstairs a single programmable thermostat it has worked for years without a problem.

However I have need to move in with mother, this older house (1954) has had two central heating systems fitted over the years, the last one with a modern combi boiler condensate type. There are internal doors and down stairs we have 5 heated areas.
1) Kitchen with just a towel rail.
2) Wet room with towel rail and underfloor heating.
3) Living room with one radiator on internal wall with TRV. Plus gas fire.
4) Bedroom with one radiator in bay window with TRV. Plus gas fire.
5) Hall which connects to all rooms, plus stairs and main entrance one large radiator on internal wall, originally no TRV only a thermostat on wall, rather draughty would be coldest room if the radiator was not so large.
Upstairs I can forget, there are three rooms and landing plus airing cupboard the latter with a radiator fitted without TRV, all rooms and landing have TRV's fitted and maintain a reasonable temperature no real problems.

However the two rooms down stairs are a real problem, living room gets morning sun, it has a bay window, and in the winter when the sun in low in the sky the temperature can rocket to 26°C not such a problem in summer, the bedroom also a bay window in morning often on the cold side, in the evening the temperature can go up, but not as bad as the living room.

Unless motorised blinds were fitted, the living room will always have a problem, all one can hope for is to minimise the problem. But fitting eTRV's has helped.

Bedroom different problem, this is more down to the wall thermostat in the hall switching off the central heating before the bedroom had warmed up.

So moving to hall, this is the root cause of most of the problems. Because wheel chair access is required there is no threshold on the front door, when the wind hits the door one can't help but get a cold draft. To compensate for this the hall radiator is large, when front door is opened the hall quickly cools down, but once shut the hall quickly heats up again.

So after some thought I have fitted a TRV to hall radiator, it now works reasonable well, when front door is opened it quickly re-heats the hall until around 18°C then the TRV starts to close so it takes quite a time to get to 19°C when the wall thermostat switches off the boiler, so far so good.

For the wall thermostat and hall TRV to work needs them to be set with around 1°C between the two devices. This means the hall has to have a fixed temperature at the moment 18 to 19°C. I can turn the wall thermostat down in the summer so acts as a frost stat, and the stop is set to 19°C so easy to turn back up when required.

However I would like to allow the house to cool down at night and heat up during the day with a peak heat in the evening. The eTRV does try to do this with living room and bedroom, but unless the boiler is running the eTRV can fully open, but radiator still does not get hot.

The answer would seem to be a eTRV in hall as well as a programmable thermostat, so the 1°C is maintained, however a standard TRV opens and closes over a range of around 3°C but the eTRV has a much narrower window. I am using MiHome eTRV at the moment which can be set to follow Nest, however I don't want it the same temperature, but one degree different.

So is there a way I can use a programmable thermostat, or is there just no way to get the more accurate eTRV to work as the poor quality TRV does, seems daft but I actually want the TRV to be poor at regulating the heat.
Rank: Project Manager
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Location: Llanfair Caereinion, Mid Wales.


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