Set Appliance State:

CH Demand
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
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

WARNING: Mains Power will be present at Overheat Thermostat and Grey wire during test.
The Boiler should not function and the Lockout Neon on the front panel should be illuminated (2).