Ferroli sigma 40 60 issue

[Gary80gas]

Im trying to fix a Ferroli sigma 40 60 heat only boiler. As soon as its powered on the main board trips. instantly. I disconnected the fan and it stops tripping, so im thinking simple enough change the fan unit. Measured the ohms and it reads 75 which sound about right. connected the fan to a plug and it runs fine and no tripping electric. Reconnect to boiler and it trips.
Boiler passes basic electric tests. Would that still trip electric board?

To be sure I checked the voltage coming off the pcb which I believe should be 240v.
At the pcb pins it is supplying approx. 130v at the cable connection ends for the fan its only 20v . So PCB looking a bit fried?
So separated the powered fan and powered boiler do not trip board, put together they trip the electric. Can anyone explain this?

 

[EvilDrPorkChop]

My first thought would be is something shorting from the fan to the casing? When you say trips, is it blowing the fuse on the board or the fuse spur.

 

[Gary80gas]

Its not blowing any pcb board fuses and the 3 amp in the fuse spur that powers the wiring for the boiler and programmer is fine. The main electric fuse box for the house is what is tripping. Just the circuit that feeds this part of the house.

The problem is obviously linked to the fan boiler earth because it stops tripping when I disconnect the fan earth. I wired the fan into the same ring circuit on a 3amp plug and it ran the fan without tripping, so on a different earth wire the fan appears ok?
If the fan boiler earth cable was 100 per cent would it still trip?
Could the cables be ok but a bad connection on the pcb trip the main circuit when the fan earth is connected? Fan or Cables or PCB?

 

[Gasmk1]

could be earth leakage to the board as when you take it out out it would would work ok as your circuit may not be looking for any earth leakage