The room thermostat will not start the boiler or control the heating in the house. The thermostat has been replaced (twice just to be sure). You can hear the thermostat clicking as it should. The hot water turns the boiler on and off as usual, and when the water is called to heat then the heating works, so we control the heating via the thermostat on the hot water tank. Not ideal but it works!! The 24 hr programmer is working as it should. Can anyone help???
The thermostat does not connect to the boiler direct but connects to a motorised valve which in turn connects to the boiler on older systems. The idea is the valve must open before boiler turns one.
Inside the valve there are micro switches which have many functions from setting valve in mid position to switching boiler on and off. Although there are generic diagrams these miss out the internal wiring of the valve so it is had to test due to back feeds.
There is often a leaver on the valve to set to mid position to bleed the system some times latching this leaver will get central heating running but as summer comes it means radiators get hot when only domestic water is required.
So I would say 70% chance a new electric head on the motorised valve will cure the problem.
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