baxi solo 3 pfl 80 pilot light ok but gas comes on with a boom?

I had a similar problem with a freinds baxi bahama 100 combi. The boom is most likely a delayed ignition of the gas or too much gas at start up. Our problem was tracked down to the spark unit coil in which the HT volts had gone weak. This meant that instead of a healthy spark it had a feeble one which led to intermittent delayed ignition. Changing the ignition unit did wonders.

Alan
February 2008