Would reversing polarity of electrical supply blow circuit board in an Idea?

We recently had a new electric consumer unit fitted. Afterwards our Ideal Classic LXFF&FF boiler had a fault, circuit board blown. Gas engineer diagnosed reverse polarity of supply had blown board. Electrician reinstated supply with correct polarity but disputes that the reverse polarity would blow the circuit board as they have built in protection diode. Can anyone give a definitive answer please?