Set Appliance State:
Mains Power Off
Set Multimeter to AC Volts 
CH Demand
Selector Switch to Hot Water and Heating
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Measure voltage across mains neutral and
black wire of connector X9 on PCB (3).
Note:
On some appliances the incoming terminal strip is located differently and has been rotated through 180° from the one shown.
black wire of connector X9 on PCB (3).
Note:
On some appliances the incoming terminal strip is located differently and has been rotated through 180° from the one shown.
Isolate as per TOPs P4
and refit as necessary