Set Appliance State:
Mains Power Off
Set Multimeter to AC Voltage 
Boiler Thermostat set to its '0' position
All External Controls calling for heat
All External Controls calling for heat
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
FULLY PUMPED SYSTEM
Measure the voltage across the Live (Brown) wire marked MAINS (L) and the Neutral (Blue) wire marked MAINS (N) on the main connector block.
GRAVITY DHW SYSTEM
For the Gravity System no permanent live is required for the boiler, measurement of the main power supply will have to be taken at the mains power Input terminals of the clock/programmer installed.
Measure the voltage across the Live (Brown) wire marked MAINS (L) and the Neutral (Blue) wire marked MAINS (N) on the main connector block.
GRAVITY DHW SYSTEM
For the Gravity System no permanent live is required for the boiler, measurement of the main power supply will have to be taken at the mains power Input terminals of the clock/programmer installed.
Isolate as per TOPs P4
and refit as necessary