Are Furnace Limit Switches Universal? Facts You Should Know

Furnace Limit Switches

Furnace limit switches are a must-have for heating systems. They regulate the furnace temperature and control the blower fan – making sure warm air circulates. These switches come in two types: manual reset and automatic reset. The manual reset switch requires a button press to turn back on, while the automatic reset switch will turn back on automatically after a set amount of time. It’s important to note that not all furnace limit switches are the same, so check your furnace manual or get an HVAC expert to help if there are issues. 

Are Furnace Limit Switches Universal

Image: Furnace limit switch

Surprisingly, these switches were invented in the 1980s as a safety measure to avoid carbon monoxide poisoning. Nowadays, furnaces are equipped with safety controls and technologies like integrated control modules and flame sensors. Knowing how your furnace limit switch works is key to preventing risks and keeping your HVAC system running smoothly. Also, regular maintenance is a must.

Furnace Limit Switches

Furnace limit switches are very important for keeping your home’s temperature regulated. They are found near the heat exchanger or warm air plenum. Their purpose is to turn the furnace blower fan on and off, depending on the temperature changes. This prevents the furnace from overheating, as well as cold air from damaging the system.

There are various kinds of limit switches available. 

  • The fan limit control switch runs the blower fan with warm air until a temp setting is reached, then turns off when the heat source ends. The adjustable fan control dial lets you set airflow to your liking.
  • High limit switches protect the furnace from overheating by shutting off the gas burner
  • Manual reset limits must be reset manually if they trip due to overheating.

The concept of a furnace limit switch dates back to the earliest days of heating systems. Back then, there was no way to monitor temperatures inside them. This caused many house fires, resulting in numerous deaths each year. People eventually developed flame sensors and safety circuits to prevent such tragedies.

Importance of Furnace Limit Switches

  • Furnace limit switches are essential for controlling and regulating air temps and airflow in your heating system
  • They protect against overheating, which can damage your home and create dangerous situations like fire and carbon monoxide poisoning. 
  • Without them, your furnace could overheat and require costly repairs. 

Knowing how they work is key to ensuring a comfortable and safe space.

Limit switches come in many forms. Disc type, snap disc, manual reset switch, and integrated control module – each designed for a specific purpose.  Regular maintenance is important for sufficient airflow within the plenum and preventing short cycling. Think: replacing air filters, cleaning burners or flame sensors, checking electrical connections, and looking out for strange smells or sounds.

Are Furnace Limit Switches Universal

Image: Common Location of limit switch in a furnace

Common Problems with Furnace Limit Switches

Furnace limit switches are essential for safety. They regulate temperature, preventing the heat exchanger and other furnace parts from overheating. When the temperature rises, the switch shuts off the heating system to avoid damage or fire.

If you’re experiencing irregular warm air from your HVAC, it’s likely due to a malfunctioning switch. This can cause the fan or blower motor to keep running when the furnace burners shut off. Causes could be a dirty air filter, inadequate airflow, a faulty fan control, or overheating from improper cycling.

To properly diagnose and fix this problem, you’ll need instructions for your furnace model’s switch. 

  • Cleaning your air filters regularly helps maintain clean air flow. 
  • You may need to replace broken bits like bimetal springs or safety circuits, and check plenum covers.

Modern furnaces have control modules with diagnostic LEDs that flash codes. Look at your furnace manual for help. Otherwise, it’s best to hire an HVAC technician to stay safe during repairs. 

Troubleshooting and Repairing Furnace Limit Switches

Limit switches are essential for any furnace to work safely and efficiently. If your furnace has issues with temperature control or the blower fan, a faulty limit switch could be the source. Here is a guide to troubleshoot and repair furnace limit switches.

  1. Identify the type of limit switch in your unit. There are two types: manual reset and auto-reset.
  2. Read your furnace manual for info on your high-limit switch location and parameters.
  3. Use a VOM or multimeter to test if your limit switch is working. It should show continuity when cold and an open circuit at the limits.
  4. Check that safety circuits, like the temp sensor probe, blower motor interlock, combustion air switches, etc., are working.
  5. Clean or replace air filters if insufficient air flow is causing overheating. Or, increase supply air plenum with dividers or plate dampers to optimize airflow.
  6. Get professional advice if you can’t repair component damage.
Are Furnace Limit Switches Universal

If too many clicks during one cycle, overheating due to blocked off baseboard grill openings behind couches or shelves, could be causing short cycling.

Bimetallic springs can wear out over time, even with quality products like Goodman furnaces. Checkups will help keep performance at its best. Follow these tips to keep your furnace limit switches in top shape for longer.

Tips for Maintaining Furnace Limit Switches

Maintaining furnace limit switches is essential to keeping your home’s heating system functioning correctly and avoiding damage. To help you keep your limit switches in optimum condition, here are three easy steps:

  1. Regularly inspect and clean the air filter in your furnace. A blocked filter can cause inadequate airflow, resulting in the limit switch tripping due to overheating.
  2. Keep the furnace housing spotless. Dust, debris, or buildup inside the unit can also cause overheating, leading to limit switch issues.
  3. Arrange regular maintenance with a professional HVAC technician. They can check all components of your heating system, including the limit switches, for any signs of deterioration or damage that may lead to future problems.

Be aware that different furnaces may have different types of limit switches – some need manual resetting while others reset automatically when the internal temperature returns to normal. If you’re uncertain which type of switch your furnace has or how to access it for maintenance, read the furnace manual or contact a specialist for advice.


Furnace limit switches are crucial for HVAC systems. They control temperature settings and prevent overheating or damage to furnace parts. These switches also help stop safety hazards like carbon monoxide leaks or fires caused by overheating components. Checking them regularly and maintaining them can stop issues and keep the heating system running smoothly.