Set Appliance State:

Mains Power Off
CH Demand
Selector switch in winter position
Timer switched to FIX ON
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Does the yellow LED light on front panel and can sparking be heard or seen?
Note:
If lockout occurs (red LED ON), reset by pressing the red lockout reset button.