Set Appliance State:

Mains Power Off
Mode selector switch to Off/Reset position
Set Multimeter to AC Volts Set meter to measure AC Volts
Hot water temperature control set to maximum
Central heating temperature control set to maximum
WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Mode selector switch to CH position.
Test 1.
Measure the voltage across brown wire on connector M11 on the main PCB and a suitable neutral.
Turn hot water tap On.
Test 2.
Measure the voltage across black wire on connector M11 on the main PCB and a suitable neutral.