Set Appliance State:
Set Multimeter to AC Voltage 
Isolate Mains Power to appliance as per TOPs P4
Mode Switch in LOW position
Disconnect and MAKE SAFE one of the Grey spaded wires (1) from the Overheat Thermostat
Mode Switch in LOW position
Disconnect and MAKE SAFE one of the Grey spaded wires (1) from the Overheat Thermostat
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
WARNING: Mains Power will be present at Overheat Thermostat and grey wire during test.
The Boiler should not operate.
Measure the Voltage across the two Red wires (both connections marked L/O) at PCB connector PL4 should be approximately 240 V AC.
The Boiler should not operate.
Measure the Voltage across the two Red wires (both connections marked L/O) at PCB connector PL4 should be approximately 240 V AC.
Isolate as per TOPs P4
and refit as necessary