Set Appliance State:
Mains Power Off
Set Multimeter to DC Volts 
DHW Tap Off
Summer/Winter Selector to Summer
Summer/Winter Selector to Summer
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Press reset to cancel purge cycle countdown.
Measure the voltage across connections 3 (blue) and 6 (orange) at connector X17 at the PCB.
Expected voltage less than 4 volts DC.
Measure the voltage across connections 3 (blue) and 6 (orange) at connector X17 at the PCB.
Expected voltage less than 4 volts DC.
Isolate as per TOPs P4
and refit as necessary