Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
Turn Hot Water Tap On
Gain access to PCB (use Insulation Mat as required)
Remove 4 wire connector from fan and make safe
Remove 4 wire connector from fan and make safe
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure the DC voltage between pin 17 on connector X20 and a suitable earth.
Expect a reading of approximately 22 Vdc.
Expect a reading of approximately 22 Vdc.
 connector x20 on pcb.gif)
 pcb in situ.gif)
 gas setup and fan.gif)
Isolate as per TOPs P4
and refit as necessary