Is Your Furnace Plenum Thermostat Or Limit Switch Tripping Excessively? 4 Possible Causes

During winter, you heavily rely on your furnace to warm up your house. However, some parts of a furnace may malfunction, rendering the unit inefficient and inoperable. You should reset your high limit switch if it trips once when the furnace is in operation. The switch may continue to trip despite constantly resetting it, indicating that the furnace is defective. If this persists, you should hire a furnace repair expert to inspect and repair it. Below is why your heating appliance's high-temperature limit switch won't stop tripping.

Your Appliance Turns On and Off Too Frequently

Short cycling implies sudden excessive variations between heating and cooling cycles. These cycles happen successively, prompting the system's high limit switch to trip. Additionally, short-cycling occurs if there is excessive or insufficient heat in the air ducts during every cycle, resulting in overheating. As a result, the switch will trip. Therefore, you need an expert to calculate your load factor and recommend the right size of furnace for your home.

The Flame Sensor Rod Of Your Heating Appliance Is Dirty

A flame sensor rod ensures that the gas valve only opens during combustion. Airborne particles may stick to the flame sensor, after which they burn and thereby cause carbon accumulation. Since the sensor's tolerance when it comes to reading variations is low, it may not read the proper level of micro amps, causing the high limit switch to trip. It is imperative to hire an expert to clean the appliance's flame sensor rod, and if it does not detect resistance discrepancy, they should replace it.


The high limit switch may trip when your heating appliance's interior temperature gets too high. Overheating may occur when the airflow is restricted in your heating appliance. Dirty filters, clogged vents as well as air ducts can lead to overheating, causing excessive tripping of the switch. Therefore, hiring a specialist to service the furnace regularly is necessary. A clean system ensures sufficient air passes through the air ducts hence preventing overheating.

Defective Limit Switch

A limit switch regulates your furnace's temperature by activating and deactivating when it reaches unsafe levels. However, the limit switch eventually becomes worn out, resulting in unexpected shutdown. If the switch trips severally, it may trigger the system's lockout mode. You should contact your technician to repair or replace the switch to ensure that the furnace is fully functional.

Attempting to fix a heating appliance on your own is potentially dangerous. Therefore, if your furnace temperature limit switch won't stop tripping, you'll need to hire a furnace expert to troubleshoot your entire heating system. Look into heating services near you.