Set Appliance State:
Mains Power Off
Set Multimeter to AC Volts 
CH Demand
Selector switch to heating and hot water position
CH temperature selector to maximum
DHW temperature selector to minimum
Clock in timed mode in an on period
CH temperature selector to maximum
DHW temperature selector to minimum
Clock in timed mode in an on period
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
Measure voltage across terminal 3 on external control terminal block marked room thermostat, and the neutral connection on the main terminal block marked N on the PCB.
Isolate as per TOPs P4
and refit as necessary