One of the most common causes of a furnace shutting off unexpectedly is low airflow. If your furnace keeps turning off, check for issues such as: Dirty Air Filters. A clogged filter restricts airflow, causing the furnace to overheat.
Insufficient airflow into the furnace
For the burners to ignite, they need airflow. The airflow into the furnace comes from the blower fan that draws air through the return air ducts. But if this airflow is choked off because of a clogged furnace filter or faulty blower, the burners may not be able to stay on for long.
Blocked vents or a clogged air filter may cause your furnace to run and then shut off too early. It's easy to fix these issues on your own. You should change your furnace filter at least once every three months. Follow our guide to do it yourself.
When your furnace starts and stops, it could be an indication that you have insufficient airflow. If there is inadequate airflow, the heat exchanger in the furnace will frequently heat up. This problem is more likely to occur if the heating unit is in a congested storage area.
This can be caused by a couple of possibilities. It's not that you're blower is out of sync, it is either going bad or if this is an older furnace with a fan-limit switch, it is cooling down the heat exchanger too fast (or the unit is underfired) and the fan switch is turning it off.
Furnaces need cold air for the heat exchanger to heat up. If there isn't enough coming in, the system will shut itself off as a safety measure. Once the internal temperature within your furnace stabilizes, it will kick back on again. However, the dirty air filter forces the furnace to repeat this short cycling.
On your thermostat, look for the fan settings. There should be two, “ON” and “AUTO.” If it seems like your furnace won't turn off, the thermostat may be set to “ON” for the blower. Toggle the switch to “AUTO” so your furnace's blower fan only runs during a heat cycle.
The top causes to blame when a furnace kicks on and off are: The air filter needs changed. The thermostat batteries need to be replaced. Blower motor malfunctions.
If the burners visibly ignite, but then go out after approximately 6 seconds, this may indicate a dirty flame sensor. Multiple failed ignition attempts will typically generate an "Ignition Failure" diagnostic on the ignition control board.
Ask twenty professional HVAC contractors the question, “How Much Does A New Furnace Cost?” and you'll probably get the same answer... “It depends.” On average, the cost of a new furnace can range from $2,000 - $14,2001. However, factors like furnace efficiency, type, size, and much more can impact this range.
Short cycling is a common sign of a bad flame sensor. The sensor thinks that there isn't a flame, so it shuts off the gas as a safety mechanism. Except, there is a flame and without the gas to supply it, it dies. This is a frustrating problem, but an HVAC technician can fix it.
There are multiple reasons why your furnace is short cycling. These could include a dirty filter, blocked vent, or malfunctioning flame sensor. You can switch for a clean furnace filter, or have your HVAC technician resolve a more complicated issue.
One of the leading causes of short cycling is an oversized furnace. If your heating system is too powerful for your home's heating demands, it will quickly heat your living space, causing the thermostat to reach the set temperature and signal the furnace to turn off.
You've left the same air filter in place for too long
Dirty air filters are perhaps the most common reason that furnaces fail to provide enough heat to a home. (They're behind plenty of other problems as well.) Over time, this air filter will become clogged with dust, dirt, and other debris.
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.
Leave the breaker(s) off for at least 10 minutes while the system is off and “rebooting.” After 10 minutes have elapsed, go back to the breaker box and flip the HVAC breaker(s) back on.
One of the most common causes of a furnace shutting off unexpectedly is low airflow. If your furnace keeps turning off, check for issues such as: Dirty Air Filters. A clogged filter restricts airflow, causing the furnace to overheat.
Your Furnace Has A Dirty HVAC Air Filter
Having a dirty air filter in your furnace can cause short cycling. While a faulty flame sensor will lead to an immediate shut-off, a dirty filter will allow your furnace to run for several minutes and then shut down.
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.
Uneven Heating
Inconsistent heating patterns often point to thermostat inaccuracies, as the device struggles to regulate the temperature evenly. On the other hand if the entire house feels uniformly cold then the furnace might be the problem.
But when your furnace won't shut off, the thermostat is often the first place to inspect. A common issue is incorrect settings. Make sure your thermostat isn't set to a constant “heat” or “on” mode, which can cause the furnace to run continuously.
Replacing a Thermostat. You'll pay between $15 and $300 for the unit in addition to labor ($65 to $100 per hour) to replace an old thermostat with a new one.