Set Appliance State:
Mains Power Off
Set Multimeter to DC Volts 
DHW Demand
DHW Selector in Maximum (+) position
CH Selector in Minimum (-) position
ON/OFF Switch in ON position
DHW Selector in Maximum (+) position
CH Selector in Minimum (-) position
ON/OFF Switch in ON position
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure voltage across the black and green leads of the plug attached to the fan.
When the fan starts the voltage should be approx. 1.5 V DC and as the fan ramps up the voltage should rise to approx. 1.9 V DC.
When the fan starts the voltage should be approx. 1.5 V DC and as the fan ramps up the voltage should rise to approx. 1.9 V DC.
Isolate as per TOPs P4
and refit as necessary