Central heating only works once hot water is called for

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6 Dec 2009
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Flintshire
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United Kingdom
Ok Guys

The heating was playing up the other day, so had the pump changed by a plumber.

Then we noticed that the heating would only cut in once the hot water was called for(i.e. tonight no central heating, ran hot water for a while and boiler and pump cuts in and heating comes on!!!!).

I have a "y" plan system with a 3 way valve (Drayton Mid position), I have noticed the leaver on the valve stuck hard to the right when malfunctioning occurs but is then free when system starts up when hot water is called for.

I have removed the actuator head and operated the wall stat and the actuator moves, I can turn the valve spindle by hand but only a very small amount 20-30 degrees. Do you think the problem is with the actuator and not with the pump as first thought?
 
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The fault causing this issue won't be with the pump. You need to check with a multimeter (not a neon screwdriver) set to AC volts, with one probe connected to the neutral terminal for all tests.

With hot water off at the programmer and heating on at the programmer and room thermostat turned up, you should get:
240V on grey wire of valve
240V on white wire of valve
240V on the orange wire of the valve
The valve should be motored fully over to heating only.

I expect you don't have 240V on the orange wire, this is what switches the boiler and pump on when the valve is at heating only. It's possible the microswitch inside the valve actuator is faulty, or the mechanism is broken or worn out inside the actuator. If you don't have 240V on the grey wire, the valve will only go as far as the mid position and will not go far enough to operate the microswitch that switches on the boiler and pump.

The valve spindle only moves a small amount as you describe.
 

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