Set Appliance State:

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

Observation:

Allow boiler to operate for CH and system to begin to warm.
Measure the differential between the flow and return pipes.
Differential should be approximately 20°c or lower.
Notes:
1. To reduce time taken for this test you may wish to turn off some radiators.
2. Differential may be higher on initial demand.