Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Disconnect the rectification lead (front lead of the three electrodes)
and the flame sense ground lead (below the safety sensor) and make safe
Ensure NO demands
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Reset appliance.
If the appliance begins its self check mode ensure it is set to ECO.
Does the appliance now reset and enter standby or does it still go to fault code?