Heating electrics is a mindset all of its own to be fair. Sparks and heating both can screw up.
Went to an evo install the other day - customer a sparks. left the wiring to the heating man (lovely pipe work). Neither had twigged the boiler needed volt free switching.
Took out the boiler controller and the honeywell relays
Made a hefty bang too when it went. Damaged the connectors on the wiring loom too. 
Went to an evo install the other day - customer a sparks. left the wiring to the heating man (lovely pipe work). Neither had twigged the boiler needed volt free switching.
Took out the boiler controller and the honeywell relays