Compact 75E pump continual ON? Help!

I have Compact 75E combi boiler and the pump is continual on! The heating and the hot water works fine but the pump stay on continually even when not require.

I have two plumbers over and they have not been able as of the to find the fault. Do you have any ideas what could cause the pump to continually run?

thanks

Paul

Compact has two diaphragms one for HW and the other for CH. Its usually the HW one that gives the trouble, but if the CH one has failed (its the one on the left) then the pin may be stuck out and keeping the microswitch activated therefore keeping the pump running.

You need a star driver to get four screws out after you have removed the clip that hold the micrswitch on, isolate the Flow/return and drain the boiler (not the whole system) The diaphragm is inside, and should be renewed as they are not that good quality. then free off/clean the pin (abrade the pin lightly with wire wool if stuff is stuck to it and lubricate it with silicone grease so it slides easily)

re-assemble & bobs your uncle. these days it takes me about 25min..used to take me and hour and a half when i was new on the job.

Edit: There is just an outside chance that it is just the microswitch that has failed in "on" position. Before you dismantle the diaphragm unclip the microswitch and test it by pushing a small screwdriver gently into the hole. you will feel it click..though its only a tiny click..if it switches the pump on and off you know you are on the right track

let us know if i'm right

Alfredo