Set Appliance State:
Mains Power Off
Mode selector switch to Off/Reset position
Set Multimeter to AC Volts 
CH Demand
Central heating temperature control set to maximum
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Mode selector switch to CH position.
Measure the voltage across the connection 2 on connector M16 on the main PCB and a suitable neutral.
Notes: Connections are numbered top to bottom.
If no external controls are fitted ensure there is a link fitted between connection 1 and connection 2.
Measure the voltage across the connection 2 on connector M16 on the main PCB and a suitable neutral.
Notes: Connections are numbered top to bottom.
If no external controls are fitted ensure there is a link fitted between connection 1 and connection 2.
Isolate as per TOPs P4
and refit as necessary