experience is everything.
Customers have experience.
Boiler packs up. Experienced repair man says it is the PCB, new PCB fitted. Fault still there, Must be the fan, new fan fitted, fault still there. another PCB fitted Fault cleared.
The original fault was a short circuit in the fan which put 230 volts onto the control lines from the PCB, this fried the PCB, new PCB is then fried as the fan is still faulty. Replacing the fan does not get the boiler working because the PCB is fried.
Sometimes experience is not enough. Not wide enough to cover all possibilities.
In this case the manufacturers reimbursed the customer for the repair costs.