There are several reasons why your furnace may not turn on. The most common include a broken thermostat, gas line issues, clogged air filters, blocked ductwork, a tripped circuit breaker, and issues with the furnace itself.
The cause of your furnace not blowing hot air could be the thermostat configuration, a dirty air filter, the high limit switch, a clogged condensate line, insufficient fuel, leaky ducts, ignition problems, a blocked burner, flame sensor issues, gas valve malfunctions, a cracked heat exchanger, or a clogged coil.
If nothing's happening when you're expecting the whir of a blower, check the circuit breaker and fuse. At your electrical panel, make sure all switches related to the HVAC system are on. Reset any tripped breakers and replace all blown fuses, and your furnace should kick back on.
Checking your thermostat is the best place to start. Make sure it's set to “heat” and that you've set the temperature higher than the current room temperature. If that doesn't resolve the problem, try switching your fan to “on” to force the furnace to start working.
If your furnace won't start, first check the thermostat settings and replace the batteries if needed. Then, inspect the air filter and replace it if dirty. Make sure the circuit breaker hasn't tripped. If everything looks okay, it might be a problem with the pilot light or ignition system.
Check the Power Source Sometimes the problem between the thermostat and your furnace is as simple as replacing the batteries. Many digital thermostats use standard batteries to power their functions. Also make sure to check there is power at the furnace as well.
The first motor to come on will be the inducer motor.
Not a large motor by any means, but it's the one that gets rid of the fumes spent by the flame that warms your home. The control board and a pressure switch acknowledge that the inducer has come on and is working properly.
You can reset the ignition on your furnace simply. To do this you must cut the power to the furnace first by turning off the circuit that powers it. Once the power is off you can remove the burner door to reveal the ignitor. Turn this to “off” and leave it off for at least 5 minutes.
Check/Clean the Ignitor
A pilot ignitor coated in debris won't ignite the furnace, even if the thermostat clicks on and sends the right signal. To access the ignitor, remove the furnace's front panel. Identify whether the ignitor is dirty or clogged.
Check the circuit breaker, thermostat settings, and air filter first as these are common causes of furnace fan failure. Inspect electrical connections, listen for unusual noises, and verify proper airflow through vents during operation.
Thermostat issues are one of the most common culprits of furnace malfunctions. If your furnace isn't working as well as it should, and you've determined that other issues such as a faulty furnace heat exchanger or dirty air filters aren't to blame, you should inspect and troubleshoot your thermostat.
First, check the power switch on your furnace and make sure it's in the on position. Next, check the electrical box to see if a fuse was blown or a breaker was tripped. Replace the fuse or reset the breaker if that's the case, and you should be good to go. Check the thermostat settings.
Most likely, your furnace is making a clicking noise and not providing heat because your furnace's spark igniter is trying to ignite your pilot light or burners but is failing to do so. In other words, there's an ignition system malfunction that needs to be fixed. Otherwise, your furnace won't start.
There are several reasons why your furnace may not turn on. The most common include a broken thermostat, gas line issues, clogged air filters, blocked ductwork, a tripped circuit breaker, and issues with the furnace itself.
Furnace Not Igniting Because of Incorrect Thermostat Setting
Make sure the thermostat is set to heating and that the temperature is set high enough to actually turn the furnace on. It may be set at too low of a temperature to activate the furnace.
Once the indoor temperature drops below the thermostat's set temperature, the thermostat signals the control board inside the furnace to begin the heating process. The combustion process starts as the gas valve opens and the ignition turns on.
If the flame sensor fails, your furnace may not be able to start or may shut down shortly after starting. Common causes of flame sensor failure include corrosion, dirt buildup, or a broken wire. The gas valve controls the flow of gas to the furnace. If the gas valve fails, your furnace won't be able to produce heat.
Check your circuit breaker and make sure that the switch for your furnace is in the “on” position. Pilot light went out. If you have an older furnace that uses a gas-lit pilot light, check to ensure that the flame is burning. If the pilot light was blown out, your furnace will not ignite properly.
If your furnace's problems continue, contact an HVAC expert. Also, if you notice discoloration when you check the pilot light, get professional help. If there are cold spots in your home, even though hot air is coming out of the air vents, the issue could be different from your furnace not working.
If your heater doesn't start, chances are the problem stems from having a dirty furnace. Having dirt on your blower motor or flamer sensor could render your furnace unable to perform. When the blower motor is too dirty, it won't pass enough cool air to the heat exchanger, leading to equipment failure.