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My red grundfoss central heating pump is working continiously even when the boiler is shut down.
the header tank in the loft has hot water in it.
can anyone help solve this problem.

checkout this topic

https://www.diydoctor.org.uk/forums/view ... hp?t=13889

The pump could be running continuously because of a faulty 3 port vale, but you have given little info about your system to enable a serious reply.

Hi Plumbob,
Thanks for the reply.
My system consists of a Boiler, Header tank in the loft,
Cylinder where the pump sits and there are two motorised valves comming off the tank pipework
There is warm water going into the header tank which cant be ok
The Pump is running continiously even when the boiler is off.
When the system is on the rads and hot water work fine.

The start point is to examine the pair of two port valves. The pump is activated by either of these valves being activated. If either jams open, the pump will not be switched off and will run continuously regardless of the timeclock / thermostat. The boiler may have a pump overrun requirement, but let's ignore that for the moment.

When the system is off, and the pump is running, press the manual lever on the side of the valve. You should feel resistance as the clockwork gearbox is wound over to the manually open position. If either of the levers are floppy, and waggle freely, that valve is in the open/on position causing the pump to run. Suspect that valve.

Next turn the boiler off at the main isolator switch so all power to timeclock etc is off. Repeat examination. If either lever is still loose, that valve is jammed open.

I am of course assuming this is a new phenomenon?

Hi Plumbbob.this week the problem has come and gone.Sometimes the pump shuts down as normal.
As of now the central heating has timed out the two valve leavers have the resstance you mention but the pump is still running!

The most likely culprit is one of the two port valves. they have a micro switch in which controls the pump and it is probably this that is faulty. When the fault occurs, try operating each valve manually several times to see if the pump turns off. Try banging the valve to see if a jolt switches it off.

Other possibilities are a damaged wire, and a boiler over run circuit fault. (Not many boilers utilise this function although it has to be considered.)

Well done Plumbob. I had the same problem and so followed your advice to Steve Lawrence, and you solved my problem. Thank you.