Set Appliance State:

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

Observation:

Is the boiler currently showing the FD fault code?
Or is the fault intermittent / reported by customer.
Note:
Fault code will take approx. 1 minute to show and will only be displayed for a few seconds before boiler resets itself.