Why does the heat cycle on and off?

Author: Mr. Kip Bartell MD  |  Last update: Saturday, May 31, 2025

If your furnace keeps turning off and on, your thermostat may be the culprit. A malfunctioning or improperly placed thermostat can cause your furnace to short cycle. Common issues include: Old wiring or dead batteries: Replace batteries or old wiring to ensure accurate temperature readings.

Why does my heat stop working then starts again?

You Have a Clogged Air Filter

One common explanation for a furnace starting and stopping repeatedly/furnace short cycling is that your air filter is clogged with dust and dirt. When this occurs, the airflow to the heat exchanger becomes restricted, and the component overheats.

Why does my heat keep cycling on and off?

First check to see if your vents or ductwork are clogged with dust and debris. This slows down the airflow into your home. With less air, your furnace needs to work harder and run longer in order to heat your home to its desired temperature. And this overwork can lead to your furnace turning on and off ad infinitum.

Why does my heat keep starting and stopping?

You may simply have a malfunctioning thermostat, for instance, that is registering temperatures wrong and needs to be replaced. A very dirty air filter in a forced air heater is actually a very common cause, too, with the increased airflow resistance leading to overheating and, in turn, causing the system to shut down.

Why is my heat turning on and off repeatedly?

A furnace cycling on and off repeatedly can be caused by various reasons, from dirty filters and obstructions in ducts and registers to incorrect thermostat settings and faulty limit switches. By following the steps above, you can help prevent your furnace from cycling too frequently and save energy costs.

3 Reasons Your Furnace Cycles On and Off Frequently

Why does my heating keep coming and going?

There are several common reasons your boiler might be short cycling, which we've broken down below: Your boiler is more powerful than it needs to be. Boiler pressure is too high or too low. Your thermostat is faulty.

How to fix a short cycling furnace?

The simple solution: Turn your furnace off and check the filter. If it's dirty or it's been 3 months or more since you changed it, put a new, high-quality filter in place.

Why is my heat going in and out?

If your furnace keeps turning off, check for issues such as: Dirty Air Filters. A clogged filter restricts airflow, causing the furnace to overheat. Replace air filters every 60 to 90 days to prevent this problem.

Is short cycling bad for a furnace?

When a furnace is short cycling, it's working hard to produce heat but isn't making any, causing strain on your furnace. If left unchecked, this could cause major issues for your furnace resulting in hefty repairs.

How do I know if my thermostat is bad?

7 Ways to Tell Your Thermostat Is Broken
  1. The Thermostat Has No Power. ...
  2. The AC or Furnace Won't Turn On. ...
  3. The Heater or AC Won't Turn Off. ...
  4. The Thermostat Reading Doesn't Match the Room Temperature. ...
  5. The Thermostat Doesn't Respond. ...
  6. The HVAC System Is Short Cycling. ...
  7. The Thermostat Forgets Programmed Settings.

How do I know if my thermostat is causing short cycling?

Turn your thermostat on and wait 15 minutes before comparing temperature readings. If the difference between what your thermostat says and what the thermometer says is more than a degree, your thermostat may need to be recalibrated.

Why does my heat go off and on?

Heat Exchanger Obstruction – When the coils inside the heat exchanger are blocked by dust or other debris, the restriction of airflow could cause the short cycling you're experiencing. Thermostat – If the thermostat has shorted out or is set to the wrong settings, you could experience some short cycling.

Why does my heat keep resetting?

The most common problems are: Power outages - Power surges or outages remove power to the thermostat, causing it to restart or reboot. Sometimes, the outage can last just a second or two, and not be noticed. Dead batteries – Some older thermostats aren't hard-wired into the electrical system and run on batteries.

Why does heat cycle on and off?

Other Possible Causes of Short Cycling

If you've ruled out a dirty air filter or a malfunctioning thermostat, the problem may be caused by one of the following: Corroded flame sensor. Improperly sized heating system. Foreign objects lodged in the chimney or air vents.

Why won t my heat stay on?

Some other reasons your HVAC system won't stay on due to short cycling are incorrect sizing, frozen coils, low refrigerant due to a leak, a faulty compressor, or malfunctioning control board. These issues require the help of a professional HVAC technician to fix through heating repair.

Why does my heat turn off after a few minutes?

A furnace may short cycle when the heat exchanger is overheated, likely due to a lack of airflow. The heat exchanger is where the air gets heated. It will trip the furnace's safety switch when it gets too hot, which shuts down the operation to protect the system from dying.

What is the most common cause of furnace short cycling?

Oversized furnace

This is the most common cause of furnace short cycling. If the furnace has been short-cycling since it was first installed, it may have been improperly sized for your home.

How do I stop my HVAC from short cycling?

How To Stop and Prevent Short-Cycling
  1. Check your air filter. Believe it or not, a clogged air filter can cause a wide variety of air conditioning issues. ...
  2. Check your thermostat placement. ...
  3. Check your air conditioner's refrigerant levels. ...
  4. Replace the low-pressure control switch. ...
  5. Check the compressor.

Why does my heat keep turning off before reaching temperature?

There are four common reasons why a furnace would short cycle; It has a dirty air filter inhibiting airflow to your blower motor, your thermostat is malfunctioning, you have poor insulation, or your furnace is oversized.

Why does my furnace start and stop repeatedly?

The typical heating cycle lasts 10-15 minutes. If your furnace shuts off after a few minutes and starts more than eight times an hour, it may require repair. Common causes of furnace short cycling include restricted airflow, a malfunctioning flame sensor, or a poorly placed thermostat.

How often should a furnace turn on and off?

Generally, a furnace cycle lasts anywhere between three to 10 times every hour; however, the frequency changes depending on several factors. If your furnace is cycling on and off more frequently than it should, there could be a problem with one of its internal components.

Why does my heat keep clicking on and off?

Dirt, dust, and debris may block the bearings, and when this happens, odd noises are common. Are bad bearings your issue? If the furnace starts clicking but still heats normally, rusty or corroded bearings are a likely problem. Lubricating sticking parts and replacing any worn-out bearings should stop the clicking.

Can a bad thermostat cause a furnace to short cycle?

Thermostat Troubles Can Cause 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 does short cycling mean?

In the heating, ventilation, and air conditioning (HVAC) business, short cycling is a phrase used to describe when a heater or air conditioner cycles on and off too frequently. It signifies a problem in your heating system's proper functioning and efficiency, in which it is not completing its heating processes.

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