You will need a multimeter to test the thermostat and figure out if it is working or not. Start by setting the multimeter to read ohms. Then, place the probes on the wire terminals and monitor the outcome. If the needle in the multimeter does not move, it means the thermostat is faulty. On the other hand, if the needle moves and reads either zero or infinity, it means the thermostat is working and the fault may be with something else.