What is a Furnace Limit Switch?
The quick answer: A furnace limit switch is a long temperature-sensor probe within a mounting plate in the combustion chamber, linking multimeter probes in terminals. Its definition is a little hard to read, but its purpose is simple. A limit switch operating correctly can effectively prevent your furnace from overheating . However, a faulty furnace limit switch can be a hassle during colder months.
Is a Furnace Limit Switch NECESSARY?
Regarding fixtures that handle volatile compounds, manufacturers tend to name each component as close to its purpose as possible. This hastens the process of finding which parts are responsible for which malfunctions, for professional technicians anyway. If you have been scouring the internet for answers to conduct a furnace repair or tune-up yourself, consider calling experts for help. Read on if you are here to learn about your furnace in-depth. First, let's figure out how furnaces work to understand the purpose and pitfalls of their limit switches.
How Your Heating System Works?
A forced air furnace is a natural gas, oil, or electric installation linked to an HVAC unit for distribution. Your furnace has different intake, heating, ventilation, and output components. Within your heating system are valves, motors, and sensors facilitating combustion. Internal components coordinate the transmission of resources and signals to prevent furnace overheats, malfunctions, and other hazards while providing your home with heated air. Here's a quick rundown of its heating process: Your furnace has various links, such as intake pipes, fuel supply lines, and power sources:
- Motors distribute electricity to furnace blowers and sensors , including furnace limit switches and control panels that automate activation and deactivation.
- The gas valve discharges gas supply into furnace burners, opening and closing as required by thermostat demands.
- A furnace plenum reaches between different source and distribution pipes; blockages may deflect air flow into the furnace and result in short cycling.
- An air filter (furnace filter) prevents any debris or carbon buildup within the air inside your furnace, which may cause hazardous clogs and affect the entire burner operation.
- The furnace blower fan directs intake and discharges through chambers to begin heating, which may lead to airflow issues due to loose parts and pollution.
- The combustion chambers contain ignition components that ignite the fuel supply according to the thermostat's designated setting.
- A heat exchanger manages heat particles from one state to another, separating fuel input and breathable warm air output into the air ducts of your HVAC system.
Sensors are armed to detect a surplus in supply based on the temperature inside your furnace. The furnace limit switch is the safety feature that deploys a lockout mode for supply intake and a hard shutdown of engines.
Why is the Fan Limit Switch Important?
The quick answer: A furnace housing a functional limit switch prevents overheating. Overheating is caused by various factors and may affect one or more of your furnace's components, impacting their integrity and functions. All elements play vital roles and work in conjunction with one another. When one component fails, another overcompensates to make up for its role. Switch terminals linked to separate control panels prevent the furnace and heat exchanger overheating when the supply and demand do not align. A surplus of hot air in your furnace due to waste heat from components working overtime hinders the cohesive function of your furnace, leading to disastrous airflow issues. The furnace fan limit switch prevents the internal air handler (furnace fan or another air exchanger) from exceeding a specified temperature. A corresponding component of the furnace limit switch located inside the control board manages other materials, such as engines, to withhold power and ignition.
High-temperature Limit Switch
A furnace high-limit switch works much in the same fashion. However, it is more accurate in deploying safety measures such as a total furnace shutdown. Unlike the furnace limit switch, a flame sensor , another safety device located near the pilot light, directly prevents ignition based on the temperature inside the combustion chamber or the surface of its bearings. The furnace limit switch shuts down furnace burners when the air temperature inside the furnace is too high. Too much heat within your furnace affects intake and output, leading to pressure buildup and damaging your furnace further.
Furnace High Limit Switch for less reliable furnaces
A furnace high-limit switch is more useful for unstable heating systems . A gas furnace, especially older or poorly maintained, produces an erratic fuel supply. Its furnace blower may also affect temperature readings due to producing minimal cool air by mixing condensation with airflow. Due to poor and unreliable intake, a standard furnace limit switch may intermittently shut systems down and boot them back up. Endless repetition will eventually initiate a lockout mode, preventing any supply from coming in and any output from being produced. While routine maintenance can prevent any of that from occurring, a furnace repair specialist may recommend upgrading your furnace limit switch. It is best to upgrade your heating system and have them tuned up regularly. However, if you are still getting ready for a new HVAC unit, upgrading your furnace limit switch is a necessary first step in ensuring safe and reliable heating.
Can You Manually Adjust the Furnace Fan Limit Switch?
If your air handlers are blowing cold air against your designated temperature settings, your furnace's limit switch may have shut down the heat exchanger. In this instance, the furnace limit switch inhibited the furnace fan from delivering warm air into your vents. A furnace limit switch and its corresponding fan limit switch are predominantly automated. However, you can take measures to operate the furnace fan yourself if you think the furnace limit switch is faulty . You can manually adjust the furnace limit switch to control your heating system.
Faulty Blower Fan Limit Switch: Control Wires
Faulty furnace limit switches may be due to their wires being frayed or corrosion in their sensors. The high-voltage electricity wires connecting the furnace fan limit switch to different components may have been compromised during operations or improper maintenance. If you clean your own furnace, be careful while opening chamber doors and dismantling components. You may trip wires and cause short circuits, compromising sensors and making your furnace fan limit switch less reliable.
How Do I Know If My Furnace Limit Switch is Broken?
You need your furnace limit switch inspected by a professional HVAC technician. You can rely on your assumptions and jump to conclusions about your furnace fan limit switch and spend on a new switch when all you may need is to clean a dirty filter. OR you can reach out to professionals for help.
What to Do About a Malfunctioning Limit Switch?
A furnace doesn't only deliver heat; it impacts your air quality in many ways. Without a proper inspection, maintenance, and tune-up, your furnace may succumb to typical wear and tear a decade earlier than its life expectancy. Contact specialists if you suspect a defective limit switch or anything wrong with your furnace. They have the necessary HVAC tools and expertise to detect carbon monoxide leaks, conduct thorough internal inspections, and do everything it takes to keep your furnace pristine and functional.
How Much Does Limit Switch Replacement Cost?
It depends on the type of furnace you have. Sometimes, furnace limit switches are only a few dollars, but a high-limit switch may cost more. Some limit switches cost up to twenty or so dollars. It is a necessary safety device on your furnace, and if you have to spend on a repair or replacement cost, don't tighten the purse string for a limit switch. Please remember safety features on furnaces should only be installed by professionals. You may establish a faulty switch and be left entrusting your family's safety to a defective component.
