Set Appliance State:

Mains Power Off
DHW Demand
DHW Selector in Maximum (+) position
CH Selector in Minimum (-) position
ON/OFF Switch in ON position
Ensure the appliance is cool
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Reset the appliance.
Does the appliance attempt to ignite before returning to lockout?
Note:
Switching the mains power off and back on will not reset a lockout on this boiler.