Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Disconnect the integral timer/programmer or wireless receiver from the appliance
(this is done by unscrewing the upper panel then sliding the receiver up and out of the front of the appliance)
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance as necessary and allow boiler
to complete its self check.
If the boiler is still in ECO mode, hold
down the ECO button for 5 seconds.
Does the appliance now operate for a preheat demand?