Your furnace’s limit switch is an important safety component that ensures the system operates efficiently and safely. It controls the blower fan and prevents the furnace from overheating by monitoring internal temperatures. When the limit switch malfunctions, it can lead to a variety of issues that compromise comfort, energy efficiency, and even safety. Ambient Heating & Air Conditioning would like to explore the common signs of a faulty limit switch, why it matters, and what you can do to fix the problem.
What is a Limit Switch?
The limit switch in your furnace serves two primary functions: it turns the fan on and off to ensure proper airflow when the furnace heats the air. Additionally, if the furnace gets too hot, the limit switch shuts down the burners to prevent damage or a fire hazard. A malfunctioning limit switch can disrupt these functions, causing noticeable issues in your heating system.
Signs of a Faulty Limit Switch
• Blower Fan Runs Continuously: If your furnace blower fan doesn’t stop running, even when the system isn’t heating, it could be due to a limit switch stuck in the “on” position. This is often caused by a mechanical failure or wiring issue within the switch. If your blower keeps running, check the thermostat’s fan setting and maker sure it is on “Auto,” not “On.” Or if the fan continues to run on “Auto,” it’s likely a problem with the limit switch.
• Furnace Cycles On & Off Frequently: A faulty limit switch can cause short cycling, where the furnace turns on and off repeatedly without reaching the set temperature. This not only reduces comfort but also increases wear and tear on the system. This can occur when the limit switch might incorrectly signal that the furnace is overheating, shutting down the burners prematurely.
• No Heat or Insufficient Heat: If your furnace fails to produce enough heat, the limit switch may be incorrectly shutting off the burners. This can occur if the switch misreads the internal temperature as being too high. Check if the burners turn off shortly after ignition while the blower fan continues to run.
• System Overheats: In some cases, a faulty limit switch might fail to shut down the burners during an overheating event, causing the furnace to become dangerously hot. Overheating can lead to significant damage and create a fire risk. The furnace emits a burning smell or becomes excessively hot to the touch.
• Frequent Tripped Safety Mechanisms: If the furnace’s safety mechanisms, such as the high-limit safety shutoff, are frequently activated, it could indicate that the limit switch is failing to regulate temperatures correctly.
Causes of a Faulty Limit Switch
• Dirt & Debris: Dust buildup can cause the limit switch to malfunction by interfering with its temperature sensors.
• Wear & Tear: Over time, the limit switch can wear out due to constant use, especially in older furnaces.
• Electrical Issues: Faulty wiring or power surges can damage the switch.
• Overheating Furnace: Chronic overheating from restricted airflow (caused by dirty filters or blocked vents) can damage the limit switch.
Call a Professional HVAC Technician
If you suspect a faulty limit switch, contact a licensed HVAC professional. The can diagnose the issue using specialized tools. If needed, they can replace the limit switch if necessary. You may need to address any underlying problems causing the switch to fail, such as overheating or electrical faults.
Central Heating Furnace & Boiler Maintenance, Repairs, Replacement, Emergency Repairs & More in Springfield, Granby, Holyoke, South Hadley, Monson, Chicopee & Agawam, Massachusetts
A faulty limit switch can significantly impact your furnace’s performance and safety. Recognizing the signs early and taking swift action can save you from costly repairs and ensure your home remains comfortable throughout the heating season. If you are experiencing issues with your furnace, don’t hesitate to contact a trusted HVAC technician to diagnose and fix the problem. For help repairing your furnace’s limit switch or other HVAC services, contact Ambient Heating & Air Conditioning today.
