Set Appliance State:
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Isolate Mains Power to appliance as per TOPs P4
External controls calling for heat
CH temperature switch to minimum
DHW temperature switch to maximum
Gain access to PCB (use insulation mat as required)
External controls calling for heat
CH temperature switch to minimum
DHW temperature switch to maximum
Gain access to PCB (use insulation mat as required)
Gas On
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure the voltage at connection 1 (red wire) and connection 2 (purple wire) on connector X6 on the PCB.
Expected voltage approximately 43 volts DC.
Expected voltage approximately 43 volts DC.
Isolate as per TOPs P4
and refit as necessary