Set Appliance State:

Gas Off
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 from the Overheat
Thermostat

Measurement:

WARNING!
Mains Power will be present at Overheat Thermostat and grey wire during test.
WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure
Mains Power On
The Boiler should not operate and the Lockout Neon on the front panel should be illuminated.
Isolate Mains Power to appliance as per TOP's P4

Re-connect the Grey spaded wire on the Overheat Thermostat.
WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure
Mains Power On
The Boiler should still be in a Lockout state. Depress the Reset Switch, (located on base of the control box) for approx 10 seconds then release.
The Boiler should now reset itself and operate in the normal way.