Set Appliance State:
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Disconnect plug connector (marked ST16) from PCB
Disconnect plug connector (marked ST16) from PCB
Measurement:
Test 1:
Measure the resistance across connections 1 & 2 (blue wires).
Resistance should be approximately 30 Ohms.
Test 2:
Measure the resistance from either of the blue wires to a suitable earth point.
Resistance should be greater than 1M Ohm.
Note:
Care should be taken that probe tips do not touch each
other when taking measurement as a false reading will
be given. Also ensure that other end of leads
are connected to the gas valve.
Measure the resistance across connections 1 & 2 (blue wires).
Resistance should be approximately 30 Ohms.
Test 2:
Measure the resistance from either of the blue wires to a suitable earth point.
Resistance should be greater than 1M Ohm.
Note:
Care should be taken that probe tips do not touch each
other when taking measurement as a false reading will
be given. Also ensure that other end of leads
are connected to the gas valve.
Isolate as per TOPs P4
and refit as necessary