DIY Doctor

Two parts to central heating system and upstairs system not working?

Postby StephenB » Mon Dec 07, 2020 9:46 pm

I have just taken over my Father-in-law's house after he has been taken in to a care home with Dementia problems. He built the house himself around 40 years ago. My wife and I are trying to renovate it and have come across various problems including this one:

It has a new gas central heating boiler which works nicely. However, the radiators in the upstairs part of the house don't ever get warm. Its a big house and I have a vague recollection that father-in-law fitted some kind of device that allowed him to turn off the upstairs section. He lived alone and never even went upstairs so it wasn't a problem.

He is an ex-plumber so (I presume) knew what he was doing. His dementia means he now has no recollection of what's going on. I have spotted a separate programmable thermostat upstairs on a wall (its a Towerstat RSP) but this doesn't seem to do anything.

I'm guessing he may have a motorised valve hidden somewhere but does that seem feasible? I'd be most grateful for your thoughts?
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Postby ericmark » Tue Dec 08, 2020 3:42 pm

If not using a room the easy way is to turn off either lock shield valve or TRV on the radiator. Keeping it simple.

Yes modern houses do often have zone valves, they are to get around government requirements rather than make the heating work better, and they work by the thermostat opening the valve, then a micro switch in the valve turns on the central heating, so heating will not run until one valve is open, all valve micro switches in parallel, so valve also acts as a relay.

However there is a problem, modern central heating boilers modulate (that means the output can be turned down) and it needs this to ensure return water cool enough to gain the latent heat.

So there are two ways to control the boilers modulation, either a modulating wall thermostat which connects to boiler ebus, which is unlikely to have been used, or using the temperature of the return water and use thermostatic radiator valves (TRV) to control room temperature.

The problem with latter it will not turn the boiler fully off in summer, it would cycle on/off all summer, so a wall thermostat is fitted into a room normally kept cool, on the ground floor, with no alternative heating, and no door to outside.

But air can get into a system, and this will stop radiators from working, and so the norm is to bleed the system, so first you turn TRV off and bleed the radiator then turn that back on and turn the lock shield off and bleed the system, this both ensures both feed and return are bleed and also shows if the two pipes are blocked or not.

Often water has to be added with a loop pipe, where a sealed system.

However most likely simply either lock shield valve (often under a plastic removable dome) is off, or the TRV is off.
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