Set Appliance State:
| Isolate Mains Power to appliance as per TOPs P4 |
Set Multimeter to mVolts DC 
Gas On; Pilot On
Measurement:
Clip the negative multimeter probe on the thermostat terminal going to the nut at the back of the gas valve.
Clip the positive multimeter probe to a suitable earth point (e.g. pipework).
Use the piezo ignition to light the pilot then hold in the gas valve control knob (to maintain flame).
Measure the voltage between the terminal of the High Limit Thermostat that is connected to the gas valve to a suitable earth point.
Is the voltage measured greater than 8mV DC?
NOTE:
It is important to measure on the correct
connection, i.e. outlet to valve.
Clip the positive multimeter probe to a suitable earth point (e.g. pipework).
Use the piezo ignition to light the pilot then hold in the gas valve control knob (to maintain flame).
Measure the voltage between the terminal of the High Limit Thermostat that is connected to the gas valve to a suitable earth point.
Is the voltage measured greater than 8mV DC?
NOTE:
It is important to measure on the correct
connection, i.e. outlet to valve.
Isolate as per TOPs P4
and refit as necessary