Hot water pump runs continuously

[Jim Greenfield]

I have a Potterton Precision boiler fitted by British Gas 8 yrs ago. All good up to now but in the last few months it has failed to come on a number of times when required by the thermostat. I have had to press the reset button. The pump has also recently started to show it is running at low power 24/7 ( ie between 4 and 6 watts). Had a Corgi engineer to look at it - he says he has sorted the ignition problem (which I shall have to wait and see if he is right) but he says the pump should be on all the time with my make of boiler. I disagreed with him over this as I think it should just run on for a short while after the finish of an ON period. Can anybody advise me if I am correct please?

 

[John.g]

If you have a external circ pump can you measure the voltage at the motor terminals while drawing this low power and also have you got a A rated (Smart) circ pump?

 

[Aquarius]

What are you resetting? If your pump is failing, or has failed, and if you’re resetting an overheat situation then your pump could well be knacked.

 

[Jim Greenfield]

There is a rest button on the boiler - I used this to get the boiler to ignite when it failed to do so when demanded by my CH thermostat. The pump is external - a Grundfos - it has a range of power settings but I have is set on AUTO. If I wind it up to the max setting (50w) it still runs 24/7. When the thermost calls for heat, everything runs as it should. Sorry I don't know how to measure the voltage.

 

[ShaunCorbs]

So with all thermostats off and timer to the off does the pump run ?

 

[Jim Greenfield]

Thanks
Yes, 24 hours a day

 

[ShaunCorbs]

Yes there’s a fault there something is backfeeding the pump or there water flowing through the pump

 

[John.g]

There is a rest button on the boiler - I used this to get the boiler to ignite when it failed to do so when demanded by my CH thermostat. The pump is external - a Grundfos - it has a range of power settings but I have is set on AUTO. If I wind it up to the max setting (50w) it still runs 24/7. When the thermost calls for heat, everything runs as it should. Sorry I don't know how to measure the voltage.

If wired via the wiring centre and not from the boiler then possible zone valve micro switch problem or unlikely but may have been wired directly from a independent source.
Also the Grundfos Auto adapt mode rarely, if ever works properly and the power output rarely rises above 9 to 12 watts which normally gives inadequate water circulation, whatever mode you select IMO should result in a power output of 14 to 25 watts, you did say you had ignition problems which should be unrelated except the boiler had cut out on overheat but then should give a fault code.

Edit: just saw your post above so maybe possible that if this pump was retrofitted that someone did connect it independently but you would probably have noticed this previously.

 

[Jim Greenfield]

Thanks everybody - getting the engineer back.
John g. - pump was fitted at time of boiler installation