In the weeks before, the system had been losing pressure and needed to be topped up a couple of times a week. Subsequently identified one small leak in a radiator. A few months before, I had it serviced when the ignition wouldn't spark (explosive sound, burner wouldn't come on). Engineer said contact points were dirty. A few weeks later, no heating/hot water- engineer couldn't identify problem but thought it was a loose wire - system kicked in when he pushed a wire in.

Last night, no heating/hot water - burner wouldn't come on - pressure seemed okay but topped it up slightly. Switched boiler off and then on, pressed reset button.

Large 'bang' - water dripping down through boiler (about a litre).

Engineer discovered fan is still now full of water - seems to think it could be rainwater.

Bluey, November 2009