Set Appliance State:
Set Boiler Control Thermostat to MAX position
Set Multimeter to DC Volts 
CH Demand
Isolate Mains Power to appliance as per TOPs P4
Ensure external controls are calling for heat
Use insulation mat as required
Ensure external controls are calling for heat
Use insulation mat as required
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Allow fan to run.
Measure the voltage across the terminals with the yellow wire and the orange wire at connector PL3 on the PCB.
Expected voltage greater than 175 Vdc.
Measure the voltage across the terminals with the yellow wire and the orange wire at connector PL3 on the PCB.
Expected voltage greater than 175 Vdc.
Isolate as per TOPs P4
and refit as necessary