Set Appliance State:
Mains Power Off
Set Multimeter to Resistance 
Turn Hot Water Tap On
DHW temperature control to maximum
CH temperature control to minimum
DHW temperature control to maximum
CH temperature control to minimum
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