Sibeer, you say that you are an electrician but you have not quoted what the leakage current measures on the boiler circuit and how much comes from the boiler itself.
Deducing these faults needs careful and logical measurements.
In most cases its a combination of smaller leakage currents which sometimes combine to trip the RCD. Some say satellite receivers cause significant leakage/
Putting the boiler on an MCB only circuit usually stops it tripping.
Tony
You been on the wine again Tony ?
OP didnt say he was an electrician and the boiler isnt tripping anything