Circulationg pump runs continuously

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Gloucestershire
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I've moved into a house with a potterton suprima 40 boiler and an unvented hot water system. After a few nights I noticed that the pump runs all the time even when there are no demands for CH or HW. All the wiring seems to be going to all the right places and there are two, 2 way valves in the system (one each for CH & HW). I've changed the PCB and it's still happening. Any ideas?
 
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Common problem usually caused by one of motorised valve micro switches sticking on (the boiler and pump are powered via these micro switches). Do a search to find other recent threads dealing with this.

PS. Why do you guys throw £100 at a PCB as soon as anything goes wrong? If you've got money to throw away, get British Gas in.
 
chrishutt said:
PS. Why do you guys throw £100 at a PCB as soon as anything goes wrong? If you've got money to throw away, get British Gas in.

more like 150 unless you buy a "van spare" off ebay....BG will supply and fit one for 132 if that is the problem. :D. More than likely the hw valve or you would probably notice your rads on constantly.
 
Olski the micro switch sticks even with valves in closed position so there would be no heat going to HW or CH just around the bypass
 
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namsag said:
Olski the micro switch sticks even with valves in closed position so there would be no heat going to HW or CH just around the bypass

:LOL: yes a fair point.
 
Thanks for some of the comments. I bought a new PCB because I was lead to believe that's what was wrong with it. Apparently they have had a history of problems (not because I've money to burn). The system does appear to work fine, heat and water do come on and off when they should, the motorised valves do their job. I think the thermister on the flow pipe could be the problem affecting the pump overrun. All other things being equal, the new PCB should be working correctly so I can only assume it is a component connected to this at the boiler that is at fault, as the pump is obviously powered from the boiler.
 
Did you notice the previous replies to your question Ade :?: :idea:
 
chrishutt said:
problem usually caused by one of motorised valve micro switches sticking on
The micro switches are on the motorised valve! Look at control circuit diagrams on Honeywell site for example.
 
Okay - I'm reading everyones comments. The motorised valves work just fine. If the micro switch was sticking would this still happen? If however I disconnect the thermister the pump then stops but obviously the boiler won't fire up.
 
Ade_Q, when one or both of the motorised valves are open, the orange wires from them to the boiler are live. Hence the boiler/pump works. When both motorised valves are shut, the orange wires should be dead. Therefore the boiler will not fire and the pump will only run on an overrun basis. Can you confirm that the orange wires are dead in this situation?
 
The boiler would fire up and keep itself hot. It wouldn't need to be on a lot for that, but you'd notice it I expect.

To check if it's the boiler or not disconnect the switched live at the boiler. The pump should stop! Also you should be able to check for mains on Sw L and Pump L with a meter, or a neon screwdriver at a pinch.
 
Chrishutt - just tested each motorised valve, CH & HW off, Orange (and grey) both live and pump annoyingly running!
 
Chris R - if i disconnect the SW live from the boiler the pump does not stop. When I disconnect the pump live it does stop.
 

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