If your blower is constantly turning on/off when the furnace isn't heating… …you most likely have
a bad fan limit switch
. … The system uses a “temperature probe” to detect temperature changes inside the heat exchanger (see image below) and turns your blower on and off in response.
What does it mean when a furnace is short cycling?
Furnace short cycling refers to
the switching on and off of your furnace system without reaching the set temperature on the thermostat
. And for those experiencing short cycling, you may notice suddenly that your home isn't as warm as it should, leaving you and your loved ones cold and uncomfortable.
How do I stop my furnace from short cycling?
The easiest way to fix a furnace that is short cycling is to
remove the flame sensor to clean it
. Use a sponge or brush to remove the dirt from the sensor. After the part is clean, follow the manufacturer's instructions to insert the flame sensor into the furnace.
Why does my furnace only run for a few seconds?
A common reason a furnace short cycles is because
the heat exchanger, the part that heats your air, is getting too hot due to a lack of airflow
. Once the heat exchanger overheats, it trips the high limit switch, which shuts the furnace down to protect it.
Can a dirty filter cause a furnace to short cycle?
A
dirty air filter
is the most common cause of short-cycling. If your air filter is clogged with dirt, it won't allow proper air flow to the heat exchanger. That can cause the furnace to overheat and forces the high limit switch to ride to the rescue by shutting the furnace off.
Can a bad thermostat cause your furnace to short cycle?
Your thermostat could also cause the HVAC
system to cycle on and off rapidly
, a process known as short cycling. Your furnace or central air conditioner spends a good amount of energy simply turning on and off, which is why you want yours to run for at least 15 minutes at a time before shutting off.
What is considered short cycling?
Short-cycling is a term for
when an air conditioner shuts down its cooling cycle prematurely, only to start back up again a short time later
. If you have noticed that your air conditioner's compressor is turning on and off rapidly, it is probably short-cycling and you need to have it repaired.
How do I know if my fan limit switch is bad?
The most common sign of a malfunctioning limit switch is
the continuous operation of your furnace's blower
. Just as the limit switch won't allow the fan to turn on until the warm air has reached the right temperature, the limit switch also shuts down when the air cools to a certain temperature.
Why do I have to keep restarting my furnace?
If a furnace isn't receiving enough airflow, it
may overheat and trigger
the reset button to trip. Make sure to clean or replace the air filters and keep the air vents open enough for proper airflow. Occasionally, the flame sensor rod may be coated with dirt and debris, causing the furnace to shut off.
Why is my furnace coming on every 5 minutes?
A dirty filter can cause the furnace to overheat
. Short cycle time: 2-5 minutes. … If the furnace gets too hot, the switch shuts down the furnace. A dirty filter prevents a flow of fresh, cool air into the furnace to be heated and dispersed.
How do you know if a flame sensor is bad?
- The furnace lights but then shuts down after a few seconds (short cycles)
- The porcelain on the flame sensor is cracked.
- The flame sensor is sooty or corroded.
How do I know if my furnace is short cycling?
- Thermostat Is Malfunctioning. If your thermostat is malfunctioning, it will give incorrect readings to your furnace. …
- The Area Around the Furnace Is Hot. …
- Short Bursts of Heat.
How do you know if your furnace is overheating?
- You notice a “hot” or burning smell coming from the vents. …
- You hear strange noises or loud humming coming from the furnace. …
- You notice the furnace cycling off without starting again.
How often should your furnace kick on and off?
On average, furnaces should kick on and turn off anywhere from
three to eight times per hour
. However, if your furnace turns on and off more frequently, don't assume the furnace is short cycling just yet.
How do you know if your furnace thermostat is bad?
- Your HVAC Keeps Turning On or Off. …
- Faulty Thermostat Readings. …
- Suspiciously High Energy Bills. …
- Constant Temperature Shifts. …
- Thermostat Is Too Old. …
- Thermostat Fails to Respond to Changed Settings. …
- Your HVAC System Short Cycles.
Can bad thermostat cause HVAC problems?
Some AC problems due to a malfunctioning thermostat
When a thermostat develops repair problems,
it will often lose its connection to the air conditioner
. In such cases, although you will need repair technicians to fix the thermostat, you shouldn't have damage to the AC itself that will need work.
