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underfloor heating thermostat

Postby JonR » Sat Oct 17, 2009 6:31 pm

A few months ago we moved into a house with underfloor heating in the bathroom.
It doesn't seem to be working, and we want to know if we're just being stupid (misunderstanding controls), or if there's a fault we can perhaps trace ourselves before calling an electrician.
Its MCB switch in the consumer unit is on. The thermostat itself is on, but appears not to be functioning. (Whatever we set it to, the floor remains cold, and there are no lights on the device itself.)
It's a plain dial - no display or name on it, but it resembles this one:
Google "" (In fact it's identical to this, except for the absence of the thermonet logo - er, and the absence of a little red light....)

If it's relevant, we also have gas central heating, with a functioning heated towel rail in the bathroom. That system has its own thermostat downstairs. We also have underfloor heating in the kitchen, with a thermostat of a different design - which works.

Of course, we could contact the previous owners for tips, but I thought it marginally less embarrassing to ask here first... :oops:
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Simply Build It

Postby ericmark » Sun Oct 18, 2009 1:49 pm

If you look [url=] Here [/url] there is a PDF of connections and it says how the resistance of sensor should be 8k ohms to 12K ohms.

My fathers had an option to use room rather than floor temperature and his under floor sensor went down. In theory they are in a pocket and you should be able to remove but in practice the old one would not come out.

If it were me I would test cables and if the sensor cable was out of parameters I would use another make of thermostat that would work on room temperature but clearly to fault find you need a meter and knowledge to use it.

To stab in the dark and try to guess what is wrong is likely throwing money away and unless you are quite good at electrics I would advise you get some one who is to do the job.

Wrong connections can do a lot a damage.

And with some systems this can cause overheating and burn out the heating cables so likely best option for you is not to DIY.
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