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Can I insulate a thermostat to get correct reading?

Postby Jamin » Fri Oct 22, 2021 5:26 pm

Hi, thanks for any advice and expertise. I’ve foolishly replaced my old analogue central heating thermostat with a digital variety. The original was mounted on the exterior of a stud wall but the new one needed to go into a back box. I duly cut a hole in the plasterboard and then it dawned on me that behind the wall is the UFH manifold for our bathroom. So now the thermostat mostly tells me the temperature of a hot cupboard rather than the hallway it was previously in. Foolish, right. I had thought I could just craft some sort of plasterboard box to sit around the back box, but wondered if there was a more sensible solution here (short of relocating the whole thing, which might well the the right thing to do, but for logistical reasons is a headache I am hoping to avoid or at least defer…) Does a fireproof box insulate from heat sufficiently, or just from flame?
Thanks all.
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Postby Zarniwoop » Sat Oct 23, 2021 8:39 pm

Sorry - no experience with the fireproof boxes so can’t comment on that but two other suggestions would be either:
a few handfuls of loft insulation pushed in to the cavity all round the back box or
use a surface patters box instead of a recessed one to keep the thermostat out of the updraft from the manifold.

Good luck - let us know how it goes.
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Postby ericmark » Fri Nov 05, 2021 2:33 am

Not sure why you replaced analogue thermostat they are better to a digital (on/off type). I would use a surface box, but do wonder if you understand the concept of a hall thermostat?

The manuals say thermostat should be installed in a room kept cool, with no outside doors, or alternative heating, and no TRV in that room, in most homes that room does not exist, so we fit a wall thermostat and a TRV in the hall.

The wall thermostat is to turn off heating in the summer, on warm days, so the TRV is set to turn off radiator before hall gets hot enough to turn off the wall thermostat, without the TRV either the lock shield valve setting would mean the hall takes ages to reheat once front door opened, or it will turn off boiler before rest of house is warm, so it needs both.

However with this house it did not work as hall is slowest area to cool, heating can be set with lock shield valve, but cooling there is nothing to set.

However in most homes the hall does cool fast enough, so idea is the TRV starts closing at around 17ºC and is fully closed at around 20ºC so with wall thermostat set at 19ºC it will not normally switch off in the winter.

The problem is if the lock shield not set correct the radiator gets hot before the TRV can have time to close, and to set the wall thermostat, TRV and lock shield to work together is hard as both lock shield and TRV head are not marked in ºC.

I found TRV set at around 2.5 was around correct setting, but I wanted to set low over night and warmer during the day, so if the wall thermostat is programmable the TRV also needs to be programmable, in last house used Energenie heads for TRV so had a current and target temperature, so if current exceeds target I closed the lock shield a tad until that did not happen, and with 4 programmable TRV heads it worked well with a modulating boiler.

This house on/off boiler so not so easy, but can still work.

I suspect you did not have an analogue thermostat, mine can be configured as analogue using OpenTherm but since oil boiler there is not option to use the analogue control. My Nest Gen 3 also has an analogue dial, I find it much easier to use to digital (push button) control, the display is digital I can set what it shows, I have it set to show temperature, but can have it to show time.

With a wall/desk thermostat in the living room it can be set to temperature required, but in the hall it is a simple any cycle device to stop boiler cycling all through the summer.

With a modulating boiler it needs to be allowed to modulate, so either a analogue thermostat connected to ebus, or it uses temperature of the return water, with latter the TRV is king.
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