Set Appliance State:

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

Observation:

Do the radiators now start to heat correctly?
Note:
If radiators still do not heat reset the bypass to its original setting.