Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to AC Volts Set meter to measure AC Volts
CH Demand
Gain access to PCB (use Insulation Mat as required)
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

Measurement:

Measure for AC voltage across external controls return pin 7 (terminal block)
and main neutral pin 4 (terminal block).
Expected voltage approximately 230 Vac.
Note.
1. Image shows appliance with no external controls fitted (external controls linked out).
2. Connection 1 of terminal block is far left when facing appliance front.