Why Does My Heater Keep Turning Off? Common Causes and Fixes

The heater keeps your home warm and comfortable during the winter. But if it starts turning on and off frequently, it’s more than just an inconvenience. This issue, known as short cycling, can strain the system and lead to breakdowns or expensive repairs. If left unchecked, it may even shorten the lifespan of your furnace.

Short cycling can happen for several reasons, many of which you can resolve before the problem escalates. Below, we’ll outline the most common causes of short cycling and how to fix them. If the problem continues, contact Superior Comfort Heating and Cooling for a thorough inspection and reliable heater repair service. 

1. Dirty Air Filters Cause Overheating

A dirty or clogged air filter is one of the most frequent causes of short cycling. When the filter is blocked by dust, pet hair, or debris, it limits airflow to the furnace. This restricted airflow forces the system to work harder and can cause it to overheat. The furnace automatically shuts down to protect itself, leading to the cycle of turning on and off frequently.

Solution: Regularly check your air filter and replace it if necessary. Most filters should be replaced every 1 to 3 months. Keeping the filter clean helps maintain proper airflow and can prevent short cycling.

2. Faulty Thermostats Lead to Incorrect Temperature Readings

Another common reason for short cycling is a faulty or incorrectly placed thermostat. When a thermostat malfunctions or is located near drafts, heat sources, or direct sunlight, it can misread the indoor temperature. This results in the furnace shutting off too early, as the thermostat signals that the set temperature has been reached, even when it hasn’t.

Solution: Check the placement and functionality of your thermostat. Make sure it’s located in a neutral area without extreme temperature fluctuations. If necessary, recalibrate or upgrade to a more reliable model for accurate temperature control.

3. Blocked Vents Restrict Airflow

The furnace struggles to distribute warm air throughout your home when airflow is restricted due to blocked or obstructed vents. This causes the system to overheat and shut off as a safety measure, resulting in frequent on-and-off cycling.

Solution: Ensure all vents in your home are open and free of obstructions like furniture, curtains, or debris. Clear any blockages to allow for proper airflow, which can help maintain even heating and prevent your heating unit from short cycling.

4. Inappropriate Furnace Size Causes Rapid Cycling

If the furnace is too large for your home, it will heat the space too quickly, causing the system to shut off prematurely. This frequent starting and stopping reduces efficiency and adds stress to the furnace, potentially leading to early breakdowns.

Solution: If your furnace is too large for your home, you must address the issue with professional help. Contact your local HVAC technicians, who can assess your home’s heating needs and recommend the correct furnace size for consistent heating. 

5. Dirty Flame Sensors Disrupt Furnace Operation

The flame sensor detects whether the burner is producing a flame. If it becomes dirty or fails, the sensor might not recognize the flame, leading to a shutdown as a safety measure. This results in the furnace turning off frequently and disrupting consistent heating.

Solution: Clean the flame sensor to remove any dirt or debris. If cleaning doesn’t solve the issue, contact nearby HVAC technicians to inspect and replace the sensor if necessary.

6. Low Refrigerant Levels Prevent Heat Transfer

If your HVAC system uses a heat pump to provide heating, low refrigerant can make it difficult for the system to transfer heat properly. As a result, the system may overwork and eventually shut down to prevent further damage, leading to short cycling.

Solution: Low refrigerant levels need to be handled by a professional. Contact our heating and cooling technicians for a heater inspection. We will check for leaks, recharge the refrigerant, and ensure your system operates optimally. 

7. High Limit Switch Malfunctions Trigger Premature Shutdowns

The high-limit switch is a crucial safety device that protects your furnace from overheating. It monitors the temperature inside the furnace and automatically shuts the system down if it detects that the heat exchanger is getting too hot. However, if the high-limit switch malfunctions or becomes overly sensitive, it can prematurely signal the furnace to shut off, even when the temperature is within a safe range. 

Solution: If you suspect the high-limit switch is causing your furnace to shut off prematurely, it’s essential to have a professional HVAC technician inspect the system. The technician will test and replace the switch. 

Enjoy Consistent Heating with Professional HVAC Services

Short cycling can lead to inefficient heating, higher energy bills, and potential damage to your furnace. Addressing common issues can prevent frequent heater shutdowns and keep your home cozy during the frigid winters. 

Call (734) 929-9820 if your heater turns off unexpectedly despite your efforts. The team at Superior Comfort Heating and Cooling will thoroughly inspect and repair so you can enjoy consistent heat all season. 

FAQs

How do I fix my heater that keeps turning off?

Check common issues like dirty air filters, thermostat problems, blocked vents, or a malfunctioning high-limit switch. If these don’t resolve the problem, contact a professional HVAC technician for a thorough inspection.

Why does my furnace turn off after 15 minutes of heating?

This could be due to a clogged air filter, an overheating issue, or a faulty flame sensor. Addressing these problems should help keep your furnace running consistently.

Why does my heat keep shutting off before it reaches the degree it’s set at?

A misreading thermostat or an issue with the high-limit switch could cause your heater to shut off early. Recalibrate or reposition your thermostat and inspect the high-limit switch.

Why does my heater turn off at night?

Your heater may turn off at night due to temperature changes affecting the thermostat, a dirty flame sensor, or blocked vents. Ensure the thermostat is placed correctly and check for other common issues.