How can I fix my Ideal Classic FF250 central heating boiler?

Hi,
We have an Ideal Claassic FF250 central heating boiler that appears to trip our RCD, leaving us with no electricity. I am convinced it is the central heating boiler causing the problem, as when the cental heating is not on, there is no problem. It is particulalrly vulnerable when firing up for the first time after being off for a few hours i.e. on a timer setting. I have been advised it could be the pump sticking, the gas solenoid valve or the room thermostat, any ideas anybody.