I am always suspicious of these questions!
They usually follow a plumber who says the boiler needs a new PCB ( without doing any tests ) and that will cost about £300 to repair.
The customer then says thank you, but no, and then goes out to buy the PCB themselves.
Unfortunately, and this part makes me smile, the fault is usually NOT the PCB but some other simple problem which a competent boiler would have ficed for under £100.
But I have no sympathy for the customer in these cases!
Tony