Set Appliance State:

Mains Power Off
CH/HW switch in HW position
Ensure that the boiler is cold and ready for Pre-heat
Boiler On/Off switch ON
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Observation:

Ensure that upon switching on the boiler ON/OFF,
the relay RLB on PCB 26 switches.
Switching can be observed through clear plastic casing of relay.