Just replaced the valves either side of a CH pump. Everything went fine until I attempted to start the heating and found that the pump would not start. The strange thing was that the boiler continued to fire without the pump running and I was under the impression that heating system worked on the principal that the controller asked the stat / which called for heat / which opened the valve / which started the pump / which fired the boiler. Therefore the boiler would not fire without the pump running. Is this wrong? Or is it simpler than that? Studying a wiring diag. it would seem that the valve controls the pump and the boiler. Which seems a bit dangerous!
You have probably got gravity hot water, which means the boiler will fire for water but the pump only runs for heating
Plumbob thanks for the reply but motorised divertor valve mounted above the pump. Turned the room stat down prior to testing, then up to switch on. Boiler starts, pump doesn't.
Assuming you've not got a boiler with pump overrun which has also developed a fault, it's highly likely you've disturbed one of the pump cable connections one end or other.
I had a similar problem once. The pump was being called to run but it had jammed. I just loosened the screw in the centre of the pump a tad, the pump started up, so I tightened the screw again... no further problems.
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