Set Appliance State:
Set Multimeter to AC Volts 
CH Demand
Isolate Mains Power to appliance as per TOPs P4
Operating Switch in Heating & Water position
Gain access to PCB (use insulation mat as required)
Operating Switch in Heating & Water position
Gain access to PCB (use insulation mat as required)
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Is there Mains voltage across connector X5 connection 2 (L Orange) and terminal block X7 connection 2 (N Blue) on Main Driver board?
Isolate as per TOPs P4
and refit as necessary