Set Appliance State:
Gas Off
Set Multimeter to Resistance 
Isolate Mains Power to appliance as per TOPs P4
Disconnect both the spaded wires (Orange wire and Blue wire) from the Reset Switch.
Disconnect both the spaded wires (Orange wire and Blue wire) from the Reset Switch.
Measurement:
Connect a multimeter across the Reset Switch spade terminals.
With the Reset Switch in the rest position an open circuit measurement should be observed.
Depress Reset Switch a short circuit measurement should now be observed.
Replace Leads after test.
With the Reset Switch in the rest position an open circuit measurement should be observed.
Depress Reset Switch a short circuit measurement should now be observed.
Replace Leads after test.
Isolate as per TOPs P4
and refit as necessary