Set Appliance State:

Set Multimeter to Resistance Set meter to measure resistance
CH Demand
Isolate Mains Power to appliance as per TOPs P4
Timer switched to FIX ON
Pull off the two black wires under the timer and note position
Selector switch in winter position
WARNING! Mains voltage is expected during test, follow TOPs P4 live testing procedure
Mains Power On

Measurement:

Measure resistance of timer contacts.
Note:
There should not be a wire on the far right hand side connector.