Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Attach FGA temperature clamps to the primary heat exchangers flow and return pipe as indicated by the red arrows
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Allow CH to run for a few minutes.
Expect a differential temperature of approximately 25°C or less.
Is the differential as expected?
Note:
The differential measured on initial firing may be slightly higher.