Set Appliance State:
On/Off Switch OFF
Set Multimeter to AC Volts 
CH Demand
Isolate Mains Power to appliance as per TOPs P4
External controls calling for heat
CH temperature switch to maximum
DHW temperature switch to minimum
Gain access to PCB (use insulation mat as required)
External controls calling for heat
CH temperature switch to maximum
DHW temperature switch to minimum
Gain access to PCB (use insulation mat as required)
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Turn On/Off switch to On.
Measure the voltage across connection 1 (brown wire) and connection 3 (blue wire) on connector X3 on the PCB.
Mains voltage expected.
Measure the voltage across connection 1 (brown wire) and connection 3 (blue wire) on connector X3 on the PCB.
Mains voltage expected.
Isolate as per TOPs P4
and refit as necessary