Pump runs when cylinder satisfied

[Wikky]

I recently moved my central heating pump so as to give me heating for my towel rail off the primary circuit. All OK except that, when no heating on, just hot water, boiler keeps firing up for a few seconds every 6 or 7 minutes. When it stops, pump continues to run. I know it's supposed to run for a while but it 's on all the time. Even when boiler is turned off (not when hot water is turned off from programmer)Towel rail is off via lockshield valve. The Megaflow cylinder only used to call for heat every 5 or 6 hours before I moved pump. Also, programmable roomstat not connected but I guess that's irrelevant?
Any ideas guys?

 

[45yearsagasman]

Please describe other controls in airing upboard ie zone valves etc.It sounds like a defective end switch in a zone valve head.Most of the modern ones can be replaced without a drain down(if the head is faulty).It may be that the valve internals are siezing and that will require a change.Your pipe alteraions are unlikely to have caused the problem.

 

[Axel]

Which boiler?

 

[Wikky]

There are only 2 motorised valves, 1 for heating and 1 for hot water. I have now tried turning the boiler t/stat right off and pump still runs continuously. It stops when I turn off "hot water" at the programmer (after a short over-run)

 

[Wikky]

It's a Potterton Suprima 60L

 

[Axel]

The pump is controlled by the boiler. Not sure if it uses temperature or timer to activate the pump overrun, but there's a clue to working out why it is coming on.

 

[twgas]

What made you think moving your pump would give you a summer rad that is working properly and in sync with the rest of the system?

 

[Wikky]

Sorry - I didn't explain things clearly. I moved the pump so as to be able to tap in to the primary circuit for the towel rail so I can have heating on in the bathroom in, say, the Spring and Autumn when I don't want the whole heating system on. It has always worked fine in every other house I've had.

 

[twgas]

Possibly the HW stat is set higher than the boiler stat.

 

[Wikky]

Yes, thanks Mick, that seems to be it. I increased the boiler temp a little and that seems to have cured the problem. Many thanks to all who responded to my query.
Clive