Set Appliance State:

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

Observation:

Reset lockout as necessary.
All heating controls calling.
Does the appliance ignite, run and diverter valve change to CH position?
Note:
CH position is when the lever is nearest to the body of the valve i.e. farthest right as look at the head when in situ.