Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
DHW Demand
Gain access to PCB
Air Pressure Sensor Plug located on right hand side of PCB
Air Pressure Sensor Plug located on right 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 Yellow wire and the neutral (blue) on the main terminal block.
Voltage should initially go to approx 3vdc Then drop down to approx 1.6vdc as the fan reduces its speed.
Voltages less than this suggest air pressure sensor not responding to fan pressure.
Voltage should initially go to approx 3vdc Then drop down to approx 1.6vdc as the fan reduces its speed.
Voltages less than this suggest air pressure sensor not responding to fan pressure.
Isolate as per TOPs P4
and refit as necessary