Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
CH Demand
Selector switch set to CH/DHW
CH temperature control set to MAX
Preheat switched OFF
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Observation:

Is the diverter valve in the CH position?
Note.
Location is behind the condensate trap, an inspection
mirror may help with observation.