Most of us have made ad hoc repairs at some time in our career but I would never encourage anyone to do so as you have, its not the manufacturers that say we cant its the HSE it is part of the GSIUR and anyone doing so could make an appliance dangerous, as you stated yourself the flame was 5cm that means absolutely nothing you neither measured the operating pressure or range rated the appliance to make sure that the appliance was operating safely, I take on your point that PCBs can be repaired but not on a gas appliance this is law not just my opinion
. This was a dry joint caused by me unplugging one of the connectors and plugging it back in once I'd dried it out.