Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Close the integral bypass by turning
the adjustment screw clockwise
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

With the integral bypass now closed do the radiators
start to heat correctly?
Note:
After a diagnosis is made and the appliance repaired ensure the bypass is reset correctly per the manufacturer’s instructions.