hi there, hope somone can help me on this one, i am a plumber although abit rusty on boiler faults due to living in new zealand for 15 years, anyway here we go.... when the control knob on the bolier is turned on it trips on the main fuse board, i have individually removed wires for pump , valves, stat, timer and wires into bolier and still it trips, the whole front panel including air switch etc have been replaced (got one cheap) still trips.When timer calls for h/w c/h and boiler is off then pump comes on but as soon as i switch boiler on it trips out not giving any time for ignition sequence to begin. gas is present at valve, haven,t heard fan come on due to instant tripping out,i am running out of ideas. please hel many thanks in advance!!! oh also when boiler etc is turned off and when i turn OFF isolating switch next to boiler this also trips main fuse board?!