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Central heating thermostat

Discuss Central heating thermostat in the Central Heating Systems area at ElectriciansForums.net

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Alan Stirrup

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Hi all, my condenser boiler central heating has started to do strange things so I set about trying to diagnose the problem. When I got to the thermostat I found that there was no power to it, could anybody tell me where this is powered from please? It is an old system, almost 30 years old so in reality it could do with being replaced but I can hardly afford to switch it on let alone replace it!
 
The power to the thermostat is likely only to be present if the time clock for the heating is set to on.
 
Alan Stirrup said:
When I got to the thermostat I found that there was no power to it, could anybody tell me where this is powered from please?
Click to expand...

You need to give us some details for us to be able to help with this.
What controls do you have for the system? Is it a combi boiler or a conventional system with motorised valves etc?
Do you have a seperate programmer/timeswitch and thermostats or something else?

Also what are you using to test for voltage? And what points did you test between?

In a conventional heating control circuit the room stat is wired in series with the CH channel of the programmer. So the room stat receives power only when the programmer CH channel is on.
 
davesparks said:
You need to give us some details for us to be able to help with this.
What controls do you have for the system? Is it a combi boiler or a conventional system with motorised valves etc?
Do you have a seperate programmer/timeswitch and thermostats or something else?

Also what are you using to test for voltage? And what points did you test between?

In a conventional heating control circuit the room stat is wired in series with the CH channel of the programmer. So the room stat receives power only when the programmer CH channel is on.
Click to expand...
Hi Dave, separate timer/thermo, conventional Baxi boiler. I’ve tried to attach pics of the thermostat but each pic was too large even with adjustments. The thermostat appear to be called T.R.A.C if that makes any sense?
 
We really need pics of the wiring both at the thermostat and preferably at the wiring centre. Perhaps you could switch the resolution of the camera down to a lower setting and retake them?
 
I’m suspicious that the connection on the right in the photo above is not a good connection.

But in general you need to follow it through one stage at a time.
Time clock. Wall stat. Zone valve (3 port) or zone valves (2 x 2 port). Pump. Boiler

There should be a junction box, usually in the airing cupboard where all of this comes together and 5-10 minutes with a 2 pole tester is normally enough to work out what is going wrong.
A photo of this box is rather important to being able to help more.
 
I’m suspicious that the connection on the right in the photo above is not a good connection
Click to expand...

Yes it looks like the screw is clamped onto the insulation. In practice there is usually continuity but it should be corrected.

The OP mentioned the boiler doing 'strange things'.... what exactly is the fault that led to investigating the room stat?
 
Thanks guys, I'll try and upload a pic of the junction box later today. That connection has been like that since the heating was installed nearly 30 years ago, the issue now is there is no power in the cables. The issue that prompted me to check the thermo was the temperature upstairs was intolerable and the pump was running continuously even when the heating had been off for several hours.
 

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