I have a problem which nobody seems to know the answer to. My boiler keeps tripping my residual circuit to earth breaker. The electrician has tested all my leads and can find no fault. The temporary cure was to change the oil pump as with the lead to the Solenoid disconnected it did not trip. This worked for about an hour after the engineer left and then failed. Both the engineer and the electrician returned. The electrician found that the lead to the pump and fan motor had been nipped and taped the lead up. After this the boiler went for about 3 days then failed again by tripping the residual earth breaker. Now it will go for about 10 minutes at a time once it cools before it trips. It will still not trip the breaker when the solenoid lead is disconnected from the pump. ANY IDEAS

Neil Stanley, February 2011

It may well be that the insulation in the solenoid is breaking down - allowing a measure of leakage which sometimes exceeds the threshold of the RCD breaker.

I have no knowledge of boilers and just a passing knowledge of electro mechanical devices... but from what you say it all points to the solenoid.

Peccavi, February 2011