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 to DHW and CH position
CH temperature selector to maximum
DHW temperature selector to minimum
WARNING! - Mains voltage is expected during test follow
TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure the voltage across the second from bottom terminal on the terminal block and a suitable neutral.
Note: If no external controls are fitted ensure there is a link fitted to the terminal block. (Link is between bottom two terminals.)