Gas Central heating Thermostat not working

  birdface 17:20 26 Nov 2011

Gas central heating with back boiler on fire.

I usually leave the heating running for 24Hours on the clock but use the thermostat downstairs to switch the heating off and on.

Occasionally switching the Thermostat on till you get the clicking noise does not work and central heating does not come on.

If I go upstairs and switch the Hot water on 24/7it starts the pump which starts the central heating.

Now could anyone pinpoint where the problem might be.

The Thermostat.The Clock or the Boiler.

It is an oldish type thermostat and not digital.Oops better add the pump as well as that does not start when switching on the thermostat but does when you switch the hot water on.

I have been known to do a bit of plumbing and electrical work but know absolutely nothing about computers.Thought that I would just add that bit on as it is true.

At the moment I don't really know what to look for or try.

And yes I know it is best leaving it to the experts which I will do if I cannot fix it myself.

  Aitchbee 17:35 26 Nov 2011

Have you checked the water pressure gauge on your boiler? The reading should be between 1 and 1.5 bar, normally. You can adjust it easily.

  pabby 17:43 26 Nov 2011

just replace it with this

  Bingalau 17:44 26 Nov 2011

Are there any batteries in the thermostat itself. Changing over to a couple of new ones does the trick in mine every couple of years.

  birdface 17:45 26 Nov 2011


You got me there.

None on mine as far as I know.

Are you thinking of a Combi System.

My Hot water and central heating are fed from a tank in the loft.

I will check the radiators tomorrow just in case it is air in the system but I doubt it.

  birdface 17:48 26 Nov 2011

Looks very similar to the one I have.But since it still clicks when you switch it on I assumed that it was Ok and the fault was elsewhere.

I will wait and see what others think before I start paying out.Thanks.

  wiz-king 17:49 26 Nov 2011

Sounds like the thermostat is on the way out. If the thermostat does not 'click' when you turn the dial then it is knackered. They are cheap and easy enough to replace. There will be three contacts on the back - comm, n/o, and n/c - (it may only use two of them) just note the which wire goes on each terminal and put then on the new one. There is often a small screw in the top of the thermostat that holds the cover on. Just make sure you turn the mains off before playing as the thermostat will/may have mains voltage on it.

  birdface 17:51 26 Nov 2011

That last one was for pabby.


I have not opened the thermostat up yet but as it is the same size as the one pabby shows I have my doubts if it will be big enough to hold batteries but will have a look in the morning when everything has cooled down.Thanks.

  birdface 17:52 26 Nov 2011


yes it still click but will have a look in the morning.Thanks.

  Bingalau 17:57 26 Nov 2011

buteman. I was tending to think that all thermostats are the same and of course they aren't. Mine is a wireless thing I think, and sends signals to the boiler in the loft. The last time my heating failled to come on I just changed the batteries and hey! Presto!

  Forum Editor 17:59 26 Nov 2011

A thermostat is just a glorified switch. When it clicks it means that the temperature in the vicinity of the thermostat is lower than the temperature at the clicking point, and the stat calls for heat.

Usually the thermostat sends its call to a boiler, and this will fire if the programmer is in an 'on' state. A modern boiler first turns on the circulating pump which pumps water through the house primary circuit, and once the pump is running the gas valve in the boiler will open and the burner(s) will fire.

If you have an indirect domestic hot-water storage cylinder it has a copper piping coil inside and this is connected to the pumped primary circuit, which also feeds the radiators. Hot water runs through the coil, gradually heating the cold water in the storage cylinder. So far so good.

Your prime suspect should be your programmer. The fact that turning the Domestic hot water side of it to an 'on' mode starts the boiler running when the heating side doesn't makes me think that the programmer has developed a fault. Either that, or the wiring to the boiler is faulty.

Replacing the programmer might do the trick, it's an easy job if you understand the principles - make sure you turn off the electricity supply before you start.

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