Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
DHW Demand
Gain access to PCB (use insulation mat as required)
Connector X4 is located on left hand side of PCB
Connector X4 is located on left hand side of PCB
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
With boiler and fan running test voltage between White wire (3) on connection X4 and the neutral (blue) on connection X1.
Expect approx 30vdc when fan funs and pressure switch makes.
Expect approx 30vdc when fan funs and pressure switch makes.
Isolate as per TOPs P4
and refit as necessary