Set Appliance State:

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

Observation:

Allow burner to ignite and establish.
Using an FGA check for Products of Combustion leaks near the burner, flue and electrode seals.
Also inspect visually for any signs of corrosion or staining.
Are all the seals satisfactory?