DIY Doctor UK DIY Forums

We have a traditional system, tank in cupboard and just had a brand new boiler fitted the other week plus last year we had a lot replaced in the tank cupboard e.g new pump, new actuator valves and a power flush. We have always got this random issue every now and again where the pump stays on even though everything is off, hot water and heating all switched off this happened with the old boiler and now the new one. Room thermostat turned right down too but it will literally stay on all night and the whole upstairs is stinking red hot and radiators piping hot. It’s quiet annoying anyone know what it could be?

Hi dn12gee,
Since this is an intermittent issue suggest either one of the motorised valves is sticking or your wiring is wrong.
Regards S

It is common for micro switches to stick with motorised valves, but for radiator to be hot it means valve must be open, but that then asks the question why only up stairs, so I wonder what plan? I have seen it where up stairs has thermo syphon heating once started but you say pump running an actuators which I would assume is motorised valves, so need more information to try and work out what is going on, is it two x two port valves or a three port valve, is there a thermostat on the hot water tank, try to identify which system is being used.

Thanks for the replies I have sent a picture of our system really hope that helps?

Hi dn12 gee,
When you have this issue what is the programmer doing? Does it show all is off. If yes try changing the programmer setting to 'off' rather than once a day/twice a day/on 24 hours.
Regards S.

The metal motorised valve seems to be central heating and the white plastic is domestic hot water, so I can see there is an indicator on the DHW one, not sure with the CH one, but the manual leaver should go slack when open and have resistance when closed.

It would seem you have a S Plan, so with valve closed the pump can't cause water to flow, I can't see a by-pass valve, the micro switches can some times stick in the motorised valves, causing the pump to run, this can burn out the pump if no by-pass valve, in the main today a by-pass valve is always fitted, as with TRV heads on the radiators they could all close, my pump is on the return and sucks the water around the system and has no by-pass valve, but it seems your pump pushes the water around so seems the valve may be missing? If there is one radiator without a TRV which is never turned off the by-pass is not needed for normal operation, but if the micro switch sticks then it can burn out pump.

So standard wiring, the programmer sends a supply to the thermostats when required, the thermostats send a supply to the valves, and the valves send a supply to boiler and pump. So a sticking switch in valve can cause pump and boiler to run even when programmer and thermostat is off.[attachment=0]S-Plan.jpg[/attachment]