Set Appliance State:
Mains Power Off
Gas Off
Set Multimeter to DC Volts 
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Upon Switching the boiler on is the voltage across connection 1 (Grey wire) and connection 2 (Purple wire) on connector CN7 on the Main Control PCB above 3V DC? After approximately 30 seconds does this voltage decrease to less than 2V DC?
Isolate as per TOPs P4
and refit as necessary