Heating Pump Tripping Fuse

Freedumb

When our heating is switched on, the circulating pump (Myson CP53) runs for a couple of seconds and then the main power fuse switch trips.

Tried switching off all other fuse switches but the heating circuit. No change.

Tried swapping the fuse switch. No change.

Isolated pump from mains and switched heating on. No trip: boiler ignited and ran as normal.

Unscrewed the pump vent plug. Rotor shaft can be manually rotated. A small amount of water dripped out when turned.

Does this sound like a pump replacement job or something more complex? I really hope this is a DIY job - a new burner for our kitchen range has just eaten our emergency fund!

The pump has gate valves.

All suggestions appreciated.

FD

knightstyle

First the "main power fuse" is not a fuse at all but almost certainly a RCD this is a detector that detects a leak of electricity from the power circuit to earth. It will trip if only a miniscule amount of leakage occurs, 30 thousandths of an amp is typical.
You probably have some damp somewhere in the pump electrics, could be condensation or a leak.
Try isolating the circuit, remove the cover on the pump electrics and drying with a hairdryer. Do the same with other components, tank thermostat for example.
Other than that get someone in to make sure the problem is the pump before replacing it yourself.
ALWAYS ISOLATE THE SUPPLY BEFORE WORKING ON ELECTRICS.

clairesdad

I had a similar problem a few weeks back. Having narrowed it down to the pump, I sourced a spare from a local heating supplies merchant, fitted it myself (easy) and was up and running within hours of original problem. The symptons of your problem were the same as mine. Electrian friend mentioned possible breakdown of internal circuitry of pump assembly. good Luck!

baldelectrician

Had this last week. When I traced the fault to the pump (with my test equipment), I opened terminal cover up and water ran out

Could have saved testing and just opened pump cover, but that's life.