I seem to have a problem with the hot water not circulating through the radiators. Its an oil system I have and the boiler will come on and will heat the hot water for the taps and bath. When the boiler is on, I think that the central heating pump also comes on as I can feel movement through it and vibration if I put a large screwdriver up against it. When the boiler switches itself off after a few minutes though, the central heating pump also switches off, as the vibration stops and the water therefore will not flow to the radiators (I know it should stay on pumping the hot water around to heat the rooms up). I looked at the room thermostat which is located in the hall and I believe that this is working ok. There is a neutral wire and 2 live wires on it and both live wires have 240v across them with respect to the neutral when the thermostat is turned up and only one of them has 240v with respect to neutral when the thermostat is turned down - suggesting that it does switch on when needed. I should point out that it is an old system with what I think is a Danesmoor boiler.
Other points that may be of interest are that I have put a digital thermometer next to the thermostat to monitor temperature and over the last few days it has never fallen below 18 degrees with the outside temperature being about 12 degrees at its lowest in the early morning.
I found the fault with the system and it was with the pump. I took the centre screw out and found that the impeller was not turning, though it would move freely. I was able to take a screw driver and after using it by spinning it in the slot was able to make the impeller eventually keep going on its own. There was a problem however in that when the thermostat switched to turn the pump off, it wouldn't come back on when needed without me spinning a screwdriver in the impeller slot to kick start it. I'm guessing that the magnetic field was no longer strong enough to start the impeller moving. I bought a new pump and fitted it over the weekend and the system is fine now.
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