Set Appliance State:
Set Multimeter to AC Volts 
Isolate Mains Power to appliance as per TOPs P4
Open the control box by removing the two securing screws and lower the access door
Draw the control board forward to allow access to the boiler control switch
Open the control box by removing the two securing screws and lower the access door
Draw the control board forward to allow access to the boiler control switch
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Carry out polarity check between terminals L and Earth and N and Earth on main terminal connector block.
Test between L and Earth should show mains voltage present.
Test between N and Earth should show mains voltage absent.
Test between L and Earth should show mains voltage present.
Test between N and Earth should show mains voltage absent.
Isolate as per TOPs P4
and refit as necessary