Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to AC Volts 
Selector Switch to Hot Water and Heating
All CH controls calling
Gain access to PCB (use insulation mat as necessary)
All CH controls calling
Gain access to PCB (use insulation mat as necessary)
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure the voltage across the black lead (neutral) and red lead (live) in the middle of connector X3 on the PCB.
Expect Mains voltage (230 VAC).
Turn DHW tap on.
Measure voltage across the black lead (neutral) and white lead (live) in the middle of connector X3 on the PCB.
Expect Mains voltage (230 VAC).
Expect Mains voltage (230 VAC).
Turn DHW tap on.
Measure voltage across the black lead (neutral) and white lead (live) in the middle of connector X3 on the PCB.
Expect Mains voltage (230 VAC).
Isolate as per TOPs P4
and refit as necessary