Fixing or replacing a thermostat is always going to be easier and less expensive than fixing or replacing your furnace. Therefore, it’s always a good idea to test that your thermostat is functioning properly before assuming something else is wrong. This article walks you through how to do just that.
First, verify that the device is set correctly. The unit should be set to ‘HEAT’ and to a temperature warmer than the room temperature in order to start the furnace. Conversely, it should be set to ‘COOL’ and to a colder temperature in order for the AC to kick on.
Next, if you have a newer thermostat, try installing new batteries. A weak battery can easily be the problem even if the back display is still lit. You should also make sure your furnace is turned on and that the circuit breaker hasn’t tripped.
Your thermostat is essentially a sophisticated switch. If the unit is set properly and has strong batteries, then it’s time to check that a signal is being sent to your furnace. This is best done with two people — one person at the programming device and the other next to the furnace. With the unit set to ‘HEAT’ and the temperature lower than the room temperature, slowly turn up the setting. The person stationed by the furnace should listen for any kind of sound. Virtually every HVAC system will make some kind of click or clack when it’s receiving a signal.
Any audible noise indicates your thermostat is probably working properly and the issue lies elsewhere. If you hear silence, however, then it’s likely you have a faulty thermostat. Replace the thermostat will usually resolve the issue.