Set Appliance State:
Mains Power Off
Gas Off
Set Multimeter to Resistance 
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
Remove plastic cover from the PCB
Remove air pressure switch connector from M3 on the PCB
Remove air pressure switch connector from M3 on the PCB
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Allow fan to run.
Check for resistance across the blue and white connections on the disconnected plug.
Expect open circuit before fan runs and short circuit (zero resistance) about 5 seconds after the fan runs (a click may be heard).
Check for resistance across the blue and white connections on the disconnected plug.
Expect open circuit before fan runs and short circuit (zero resistance) about 5 seconds after the fan runs (a click may be heard).
Isolate as per TOPs P4
and refit as necessary