Maintaining your appliances is crucial if you are a homeowner, especially when it comes to the furnace. Here are some potential problems you should be aware of in case they happen to you.

Bad Ignition Module 

Your furnace's ignition module is a small control board that just controls the gas valve, spark igniter, and flame sensor. This module can be responsible for a lot of problems within your furnace that are not so easy to troubleshoot on your own. For example, it may cause the spark to not be sent to the igniter, or not send power to the gas valve. An HVAC technician can come out to your home and test the ignition module to make sure that it is working properly. 

Bad Thermostat

Sometimes the problem is not with the furnace itself, but the thermostat that controls it. Unfortunately, it's not always easy to figure out if the thermostat is the problem unless you have a replacement thermostat on hand. One way that an HVAC technician will test the thermostat is by trying to start the furnace with the thermostat disconnected. A jumper wire can be used to connect two of the connections behind the thermostat, and if everything is working, the furnace will turn on like normal. 

Clogged Condensate Trap

Your furnace has a trap that is designed to collect condensation and uses a pump to push the water to a nearby drain. However, this condensate trap can be clogged from various debris, which will cause a pressure switch to sense that there is water in the furnace and turn the entire system off. Clearing whatever is clogging the trap will get the water flowing out of the furnace and keep it running.

Stuck High Limit or Pressure Switch

Have you noticed that the blower motor is constantly turned on, but nothing else with the furnace is working? This could be due to a high-limit switch that is stuck in the open position. The high limit switch acts as a safety mechanism by shutting down the furnace if the temperature within it gets too high. Sometimes this switch needs to be replaced with a new one when it is stuck in the on position after being tripped, and it won't turn off to allow the furnace to run again.

The same thing can be said for the pressure switch as well, which is another safety mechanism used in combination with the condensate trap. If the switch is stuck, it will always assume that there is too much condensation in the furnace and remain shut down. 

If you encounter any of these issues, contact a professional furnace repair service as soon as possible.