Triton Opal, fixed PRD but now its blown the isolation switch?

I spent 10 minutes replacing the PRD on this unit, thinking that this was a nice easy fix. When I have come to pull the cord on the isolation switch for the first time a lovely bright blue flash appeared from the switch.

I have checked that I have not shorted any internal wiring, all appears sound, and the unit has been working fine until I twisted the outlet pipe which caused the PRD to blow.

Erm, any ideas appreciated? Could the heater unit have become damaged with the pressure build up before the valve blew?

Richard Greaves
August 2007