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Roomstat for Potterton Boiler Gravity fed Central Heating System

Postby greengrass » Mon Oct 29, 2018 10:31 pm

Central heating Potterton boiler. (Gravity fed)
11 radiators all with a thermostatic valve. ‘Er indoors’ came up with this question to which I said “ I’d know I haven’t a clue”.
This is the question in two parts.
1. turning on all radiators to Number 3-4 setting on their respective Thermo control valves.
2. Turning down to frost setting all but the two in living room.
So 1 or 2?
The faulty original timer at side of the boiler was replaced for a wireless room stat. Which we keep in the hall the second coldest room in our bungalow.
Many thanks to all.
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Simply Build It

Postby ericmark » Tue Nov 06, 2018 2:08 pm

Two completely different types of boiler, old digital either on or off, new analogue on/off up to minimum output typical 6 kW then modulates the flame height until at maximum output typical 24 kW the two boilers need very different control.

With a TRV some heat comes from the radiator, electronic heads can compensate for this, but where the boiler is switching off/on all the time the TRV may stop rooms over heating but they are a bit hit and miss. And every time the boiler switches off all the heat in boiler is lost through the flue, so controlling a non modulating boiler with TRV's may not be best option,

There is nothing to stop you using more than one wall thermostat, I use two, both in parallel so if either calls for heat boiler runs, so if only using two rooms bedroom and living room you simply swap control between both rooms and use rest on frost protection only.

So a scenario two wireless programmable thermostats and two terrier i30 TRV heads, the change over times set the same on both TRV heads and wall thermostat so say 8 am living room i30 to 30°C so it will not turn off, wall thermostat at 20°C and bedroom i30 down to 16°C to maintain background heat, and wall thermostat down to 12°C so it will not switch on, at 10 pm reverse the bedroom i30 at 30°C so will not switch off and wall thermostat at 18°C and in living room wall thermostat at 12°C and i30 at 14°C to maintain back ground heat.

So with programmable TRV and Wall thermostats you can have full control of where is heated, the programmable TRV is basic being used like a zone motorised valve but much easier to fit. The wall programmable thermostat is controlling room temperature.

Above assumes boiler simple on/off, however with a modulating boiler you want the TRV to control room temperature not the wall thermostat, as you want the boiler to modulate not turn on/off. So wall thermostat needs to be in a room not used much, it's job is to turn off boiler on a warm day, not to control room temperature so common place is the hall.
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Postby greengrass » Sat Nov 10, 2018 6:23 pm

Hi ericmark thanks I'm a bit confused as i haven't a clue about c/h .
British Gas Wireless thermotat.

User side I set 21 'Actual/room is 19 sytem on 'Actual eventually matches 21' nice. ( via twin 3' rad in hall with all adjoining doors shut.

Then the time of on/off settings and the thermostat turns off. when on time is reached I have to reset the User side temp which has dropped to actual/.room temp of 19 somtimes 18 so i have to each time bring user side temprature back up OVER 'Actual/room' temp of hall to get temp up in livingroom with rads TRV's at 4 . Is that how the thermostats work ? or is there a fault on it.. Would there be any benifit in opening all TRV;s fully? and leaving them just going around once a month the keep them free from sticking.
Many thanks in advance.
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