Set Appliance State:
Set Multimeter to AC Volts 
Isolate Mains Power to appliance as per TOPs P4
CH Demand
DHW Selector in Minimum (-) position
CH Selector in Maximum (+) position
ON/OFF Switch in ON position
Ensure the external controls (if fitted) are calling for heat
Set the clock override switch to the 'I' position
Lower the facia
CH Demand
DHW Selector in Minimum (-) position
CH Selector in Maximum (+) position
ON/OFF Switch in ON position
Ensure the external controls (if fitted) are calling for heat
Set the clock override switch to the 'I' position
Lower the facia
| WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure |
Measurement:
On the 24 hr clock, to the left side of the Control box, measure the voltage across the left of the two
red leads and the blue leads (neutral).
Expect mains voltage.
red leads and the blue leads (neutral).
Expect mains voltage.
Isolate as per TOPs P4
and refit as necessary