Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to DC Volts 
Gain access to PCB (use Insulation Mat as required)
| WARNING! - Mains voltage is expected during test follow TOPs P4 live testing procedure |
Measurement:
Boiler On/Off switch On.
Reset lockout if necessary.
Measure voltage across terminals 1 (+ve probe) and 8 (-ve probe)
on the low voltage terminal strip marked ST18 on the PCB.
Reset lockout if necessary.
Measure voltage across terminals 1 (+ve probe) and 8 (-ve probe)
on the low voltage terminal strip marked ST18 on the PCB.
Isolate as per TOPs P4
and refit as necessary