Potterton Puma 100e gone dead!?

Hi, got up on Saturday morning and boiler was dead, no lights, etc. Thought it might be the fuse in the socket, so changed. Boiler came on again for a few minutes but then there was a pop and fizzing sound. Had an engineer out yesterday. he changed the fuse and surveyed the control board and said all ok, the heating and hot water worked for rest of evening, but when I got up this morning, not working again. Have topped up with water as low. The boiler is in a brick cupboard outside. I noticed one of the hinges has come away and door not closing properly - would the boiler shut down if rain has got in? Any other ideas greatly appreciated.
Thx