Understanding Limit Circuit Lockout: Troubleshooting to Prevention

Limit circuit lockouts, also known as limit circuit lockout, can be a frustrating and disruptive issue for homeowners, especially during the cold winter months when a malfunctioning furnace can leave you without heat. Understanding what a limit circuit lockout is and how to troubleshoot and prevent it can help you avoid unnecessary discomfort and expenses. In this article, we will explore the importance of the limit switch in your furnace, common signs of a limit circuit lockout, why it happens, and how to reset your furnace after a limit circuit lockout.

We will also discuss preventative measures and when it may be necessary to call a professional HVAC repair company for assistance. Whether you are a DIY enthusiast or simply want to be informed about potential furnace issues, this article will provide valuable insights and practical solutions. So, let’s dive in and discover the ins and outs of limit circuit lockouts.

The Facts at a Glance

  • A limit circuit lockout is a crucial safety feature in furnaces that prevents overheating.
  • Common signs of a limit circuit lockout include the furnace not producing heat and the blower continuously running.
  • Troubleshooting steps for a limit circuit lockout include checking the air filter, the thermostat, and the limit switch.

limit circuit lockout

1/5 The Importance of the Limit Switch

Guardian of Safety: The Indispensable Role of the Limit Switch in Your Furnace In the realm of furnace maintenance, safety reigns supreme. Enter the limit switch, a stalwart protector of your heating system, tirelessly warding off overheating and potential catastrophe. Picture the limit switch as a vigilant temperature monitor for your furnace.

Its duty is to maintain a harmonious balance, ensuring that the temperature never strays into dangerous territory. Should it detect a perilous surge, the limit switch swiftly shuts down the furnace, shielding it from harm. To guarantee the optimal performance of the limit switch, regular maintenance is paramount.

Just like any other vital component of your furnace, the limit switch thrives on attention and care. By adhering to a routine maintenance schedule, you can nurture its longevity and provide unwavering protection for your furnace. Do not underestimate the significance of the limit switch; it is not merely a minuscule cog in the system.

Rather , it is a vital safety feature, the linchpin that upholds the smooth operation of your furnace and fends off the specter of overheating. Devote the necessary effort to its maintenance, and you shall revel in the comforting embrace of a safer and more efficient furnace for years to come.

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In this video, we delve into the world of limit switch lockout. Learn how this safety mechanism works and why it’s crucial for preventing accidents in various industries. Watch now to understand the importance of limit circuit lockout.

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2/5 Troubleshooting Your Furnace for a Limit Circuit Lockout

In the quest to troubleshoot your furnace’s limit circuit lockout, there are a few crucial steps to undertake. Let us embark on this journey together, as we unravel the mysteries and find solutions. Step one: Begin by examining the wiring connections with utmost scrutiny.

In the intricate web of circuits, loose or damaged connections can be the culprit behind the lockout. Secure all connections tightly, eliminating any potential for mishaps. Step two: We must turn our attention to the thermostat, the gatekeeper of temperature regulation.

A faulty thermostat can send misleading signals, causing the furnace to overheat and triggering a lockout. Verify that it is functioning correctly, displaying the desired temperature and accurately reflecting the room’s actual conditions. Step three: Now, we delve into the realm of air filtration.

The air filter, a guardian against impurities, can become a hindrance if neglected. A dirty or clogged filter restricts the airflow, leading to overheating and, inevitably, a lockout. Regularly cleanse or replace the filter, ensuring the smooth operation of your furnace.

By following these troubleshooters’ path, you may unravel the common causes of a limit circuit lockout and potentially resolve the issue independently. However, if uncertainty lingers or expertise eludes you, do not hesitate to seek the aid of a professional HVAC technician. Remember, the key to preventing future lockouts and ensuring the longevity of your furnace lies in proper maintenance and regular inspections.

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limit circuit lockout

3 Easy Steps to Fix a Furnace Limit Circuit Lockout

  1. Check the thermostat settings and make sure they are set correctly.
  2. Inspect the air filter and replace it if it is dirty or clogged.
  3. Reset the furnace by turning off the power switch, waiting for a few minutes, and then turning it back on.

3/5 The Role of Overheating in Limit Circuit Lockouts

Regular maintenance is essential for keeping your furnace running smoothly and preventing overheating issues. By cleaning or replacing air filters, inspecting and cleaning the ventilation system, and keeping vents and registers clear, you can ensure efficient operation and avoid limit circuit lockouts. A malfunctioning limit switch can cause problems by failing to accurately detect temperature and shutting off the furnace when needed.

This can lead to overheating and trigger a lockout. If you experience a limit circuit lockout, it’s best to leave the repair to the professionals. Attempting to fix it yourself can make matters worse and even pose safety risks.

HVAC technicians have the knowledge and tools to diagnose and fix the problem correctly, including addressing any issues with the limit switch. To prevent lockouts, make sure to regularly maintain your furnace and address any problems promptly. Understand the risks of overheating, the impact of a faulty limit switch, and the importance of professional HVAC repair.

Schedule annual maintenance with a trusted technician to keep your furnace running smoothly and avoid unexpected lockouts.

limit circuit lockout

Did you know that limit circuit lockouts can be caused by something as simple as a dirty air filter?


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4/5 Preventing Future Limit Circuit Lockouts

In order to maintain the optimal performance of your furnace and avoid any disruptions, it is crucial to take certain precautions. Begin by regularly examining and cleaning the ventilation system to eliminate any dust or debris that may impede airflow. It is also essential to clear all vents and registers to prevent blockages caused by furniture or other objects.

Furthermore, it is highly recommended to schedule an annual maintenance appointment with a skilled HVAC technician who can detect and resolve any potential problems. By implementing these proactive steps, you can minimize the likelihood of lockouts, prolong the lifespan of your furnace, and spare yourself from unforeseen malfunctions.

Understanding and Troubleshooting Limit Circuit Lockouts in Furnaces

  • A limit circuit lockout is a safety feature in furnaces that shuts down the system when it detects a potential hazard.
  • The limit switch is a crucial component in the furnace that monitors the temperature and prevents the system from overheating.
  • Common signs of a furnace limit circuit lockout include the system repeatedly turning on and off, no heat being produced, or the blower fan running constantly.
  • To troubleshoot a limit circuit lockout, you can check for a dirty air filter, inspect the blower motor, and verify that the thermostat is set correctly.
  • A limit circuit lockout can occur due to a variety of reasons, including a malfunctioning limit switch, blocked airflow, or a faulty thermostat.
  • Overheating is a common cause of limit circuit lockouts, as it can trigger the limit switch to shut down the system to prevent further damage.
  • To reset your furnace after a limit circuit lockout, you can turn off the power to the system, wait a few minutes, and then turn it back on. However, it is important to address the underlying issue to prevent future lockouts.

5/5 Choosing the Right HVAC Repair Company for Your Furnace Needs

When it comes to selecting an HVAC repair company for your furnace, there are crucial factors to bear in mind. Firstly, prioritize technicians with proper certification and expertise in furnace repairs. This guarantees their ability to effectively address any issues.

Moreover, take into account the company’s reputation and customer feedback. A track record of positive experiences and exceptional service is indicative of reliability. Reading reviews can provide valuable insights into the experiences of others.

Furthermore, ensure that the company offers emergency services. Furnace problems can arise unexpectedly, particularly during colder months, necessitating prompt assistance. By carefully considering these factors, you can engage the services of a qualified and dependable company to ensure the seamless operation of your furnace.

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Possible Causes and Solutions for Furnace Issues – Tabelle

Possible Causes Solutions
Dirty air filters Regularly clean or replace air filters to ensure proper airflow and prevent overheating. Recommended frequency is every 1-3 months.
Blocked or restricted airflow Clear any obstructions in vents and registers to allow for unrestricted airflow. Ensure furniture or other objects are not blocking the vents. Regularly vacuum and dust the vents to prevent buildup.
Malfunctioning limit switch If the furnace fails to turn on or off at the appropriate temperatures, the limit switch may be faulty. Consult a professional technician to inspect and replace the limit switch if necessary.
Faulty wiring or connections Inspect all wiring and connections for any signs of damage or loose connections. If any issues are found, contact a licensed electrician or HVAC technician to repair or replace the faulty components.
Inadequate combustion air supply Ensure the combustion air supply is not hindered by keeping vents clear and unobstructed. This allows for proper air circulation and helps with efficient combustion. Regularly inspect and clean combustion air intake vents.
Improper thermostat settings Check the thermostat settings to ensure they are set correctly. Make sure the thermostat is set to “heat” mode and the desired temperature is set higher than the current room temperature. Replace the thermostat batteries if needed.
Ignition or pilot light issues If the furnace is not igniting, check the pilot light or ignition system. Follow the manufacturer’s instructions to relight the pilot light if it has gone out. If the ignition system is faulty, contact a professional technician for repair.
Fuel supply problems Ensure there is an adequate supply of fuel (such as natural gas or oil) to the furnace. Check the fuel levels and contact the fuel provider if there are any issues with the supply.
Insufficient insulation Poor insulation can lead to heat loss, causing the furnace to work harder to maintain the desired temperature. Consider adding insulation to walls, floors, and attics to improve energy efficiency and reduce strain on the furnace.


In conclusion, understanding and troubleshooting a limit circuit lockout is essential for maintaining the functionality and efficiency of your furnace. By identifying common signs, troubleshooting the issue, and knowing how to reset your furnace, you can prevent future lockouts and ensure the proper operation of your heating system. However, if you are unable to resolve the issue on your own, it is recommended to seek the assistance of a professional HVAC repair company.

Remember, we are here to help you with all of your furnace needs.


What is a limit circuit lockout?

If the limit or flame rollout switch remains open for more than 3 minutes or if there are 10 consecutive limit trips during high-heat, the lockout feature called “Limit Circuit Lockout” will activate. This lockout is a safety measure that shuts down the control system. The control system will automatically reset after 3 hours. This feature was implemented on December 30, 2017.

What is limit circuit lockout code 13?

If you encounter error code 13, also known as Limit Circuit Lockout, it indicates that the high limit or flame rollout switch is open. This occurs when the limit or flame rollout has been open for more than 3 minutes. To resolve this issue, it is important to check the furnace’s air flow and make sure it is adequate. If needed, increase the airflow to ensure proper functioning. This information was last updated on November 30th, 2020.

Why would my limit switch keep tripping?

When the air inside your furnace becomes excessively hot, the limit switch is activated to prevent overheating. If the furnace’s high limit switch is triggered due to overheating, it is an indication that there may be a problem with the airflow, which hampers the proper movement of air through the system. To address this issue, it is recommended to check the condition of your air filter and replace it if it is dirty.

What does limit circuit open mean?

When the furnace failure code shows an “open limit”, “open high temperature switch”, or “open rollout switch”, it is likely that the furnace has become too hot. In this situation, the limit switches play an important role by shutting off the burner and activating the circulating fan to prevent further overheating. By detecting and responding to high temperature conditions, these switches ensure the safety and proper functioning of the furnace.

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