How to repair my baxi solo wm40/4pf boiler?

I recently replaced the room thermostat for a new digital stat. thinking there was only 2 wires and a earth wire I couldn't go wrong! I was of the impression the stat switch was either open or closed?
When i conected the new stat, the was a bang from the boiler and the circuit breaker on the consumer unit tripped. Once reset, I noticed I had lost the electrical supply to the circuit board in the boiler. If i give the board a supply the boiler fires up but I suspect the pump is not powered as the boiler will overheat. A little knowledge can be dangerous !