Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
Main On/Off Control in the On position
Remove fixing screw from power unit and lift clear of the display board and make safe
Remove fixing screw from power unit and lift clear of the display board and make safe
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
If a fault code is displayed press boiler 'Reset' button.
Measure 5V DC across X18 Brown (+ve) and X18 White (-ve).
Measure 5V DC across X18 Brown (+ve) and X18 White (-ve).
Isolate as per TOPs P4
and refit as necessary