Increasing control of central heating.

27 Jan 2008
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Llanfair Caereinion, Nr Welshpool
United Kingdom
My mother only used down stairs in the house all up stairs radiators are set to number 1 setting on TRV or turned off where no valve fitted so only three radiators and two towel rails in use.

In real terms just two rooms one used as a bed room the other as living room both with TRV fitted. The wet room and kitchen just have towel rails and the hall has one long radiator and no TRV.

The thermostat is in the hall and the stairs have a heavy curtain to stop heat going up stairs.

The afternoon sun will really warm up the living room and wind direction also very much effects the temperatures of the two rooms. Efforts to get mother to leave doors open has failed.

So next thought is:- Electronic programmable heads for the two rooms, to get rooms to required temperature, rather than the hall, either that or some electric head and wall thermostat.

However my son is telling me the by-pass valve will fail if it operates for too long? He tells me I must have a thermostat to turn off boiler, (a Worcester combi-condensation) and I can’t use the valves on the radiator to control heat alone. With a wired head I could clearly combine the two radiators so if either one calls for heat the boiler will run but the thermostats are normally single pole which means a couple of relays or maybe a PLC I have spare.

I have tried setting the existing TRV but don’t seem to be able to get a happy medium either mum complains too hot or too cold. With my home thermostat you can press the hotter or colder buttons and at next temperature change it reverts to programmed temperature some thing like this would be ideal.

So what head can I get for the TRV and do the heads have micro switches like found in motorised valves? Will the programmable TRV be any better than a standard head at controlling temperature? And are the heads all the same or do I need one special for that make?

Yes I know could use two motorised valves but they are bulky ugly things. Heads for existing TRV would be far easier to fit.
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The system you describe was sold by Honeywell as 'Hometronic' from 1999, and a simplified, cost reduced 2014 version is now sold as 'Evohome'.

You could invent your own version but it will be 16 years too late!
At £270 it's a tad expensive.
sensor heads are £12 to £40 and although I am not looking for cheapest option I am uncertain what the extra £240 will give me. OK don't have to bend down to alter settings but both are measuring temperature close to radiator rather than at other side of room so can't see advantage.

All the units there seem to be a host of different makes seem to lack info as to what valves they fit. Some can be controlled from ones phone but my mother has a problem with TV remote never mind an android phone so it will be a case of set and then forget until batteries fail.

I think the hall radiator needs a TRV so three valves down stairs but it's the boiler and by-pass valve which I am unsure about.

I was lead to understand as each TRV closes more water is by-passed with the by-pass valve so the return water gradually gets warmer and warmer and as the happens the flame hight reduces to match.

Once it can't go any lower then it switches off for a set time then re-tries. If after initial warm up hot water is returned it increases re-try time and if not it decreases re-try time.

So in essence the boiler reads the info it gets from the TRV by measuring return water temperature no need for any general thermostat or timer.

However my son is telling me this is not the case and I need a method to switch off the boiler once all rooms are warm. This could be as simple as a series of room thermostats all wired in parallel. I intend to rewire house so wiring for central heating not really a problem.

So I could use a
Horstmann DRT2 Programmable Digital Room Thermostat in each room and a programmable TRV both set to same program and for the two rooms £75 would both switch off boiler when warm enough and control radiator but is this all required?

The problem at the moment is carers fiddling with the temperature settings. With best intentions they screw up the TRV or wind up the wall thermostat and roast my mother who then also plays and is near frozen.

The programmable units if I am right allow on to change temperature but at next program change they revert to program so within 12 hours any fiddling is cancelled.

I have walked into her living room and temperature has been 32°C clearly too hot but also found her bedroom at 16°C which is really too cold. The hall thermostat and the room TRV's seem to be battling it out without any clear winner and it's the two independent controls which are the problem.

If the living room is too warm or cold it's not the TRV that's adjusted but the hall thermostat which being the other side of a door is never going to work.

Spending £100 is great but £270 is really OTT.
Champagne ideas. . Beer money :rolleyes:

Evohome will give you a boiler interlock. So it only fires when it needs to rather than than scooting round the bypass circuit unnecessarily heating that loop and cycling the boiler even more.
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