Check with your owner’s manual for suggested temperatures. For a general guide, set the two lowest ones (from the furthest left) to 100 and 130 degrees to control when the fan comes on and goes off. The third marker should be set around 200 degrees as a safety shut-off for the burner.
How do I know if my fan limit switch is bad?
The most common sign of a malfunctioning limit switch is the continuous operation of your furnace’s blower. Just as the limit switch won’t allow the fan to turn on until the warm air has reached the right temperature, the limit switch also shuts down when the air cools to a certain temperature.
How does a limit switch work on a furnace?
A limit switch is a device that’s located under your furnace’s supply plenum. It reads the temperature of the plenum and waits until it gets appropriately warm. … If the temperature inside of the plenum gets too hot, it shuts off the gas supply to your burners to prevent your furnace and heat exchanger from overheating.
What is the main safety function of a fan limit switch?
While the primary function of the limit switch is to turn the blower fan on and off, it also has a safety role. When the temperature in the air supply plenum gets too hot, the limit switch turns off the furnace boiler to keep there from being any damage from overheating.Is it OK to run furnace fan constantly?
Running your furnace fan all the time isn’t exactly a bad thing. In fact, there’s no need to worry about the fan wearing out or breaking down because it’s designed to run continuously, and there’s an array of benefits connected to this.
Should a limit switch be open or closed?
The limit switch is a normally closed switch in series with the sail switch and the thermostat. Being temperature actuated, it is designed to “snap open” when an over temperature condition occurs. Thus the switch is normally opening under full load conditions and that causes arcing of the contacts.
What happens when a limit switch goes bad?
One common symptom of a malfunctioning limit switch is a blower fan that doesn’t shut off. … A bad switch also can prevent a furnace from operating at all. If the switch has completely failed and is stuck in the open circuit (off) position, the furnace won’t run. The same effect can result from repeated overheating.
Can you run a furnace without a limit switch?
Without a functioning furnace limit switch, a furnace would not be able to regulate the temperature in conjunction with a thermostat. Typically, a furnace limit switch consists of an exterior plate and a temperature probe that lives inside the furnace housing.Where is the fan limit switch located?
Your fan limit switch is located inside the furnace panel cover, usually near the upper right corner. The fan limit switch is responsible for turning the blower on and off at the appropriate times.
Why does my limit switch keep tripping?If the air inside your furnace gets too hot, the limit switch trips to prevent overheating. If the furnace high limit switch trips due to overheating, there is likely an airflow issue that is preventing proper air movement through the system. … A dirty filter is the most common cause of airflow issues.
Article first time published onHow do you know if your limit switch is bad on your furnace?
Troubleshooting Limit Switch Problems If it fails in its first function, it doesn’t signal the blower motor to start and/or stop properly. If it fails in its second function, it shuts off the gas when there is no danger of overheating, and the furnace stops producing heat.
Is it better to have furnace fan on auto or on?
Keeping your fan on AUTO is the most energy-efficient option. The fan only runs when the system is on and not continuously. … If your fan runs continuously, moisture does not have a chance to drip outside. It blows back into your home and your AC works hard to remove extra moisture from the air.
Do fans run up electric bill?
3. Unnecessary Use Of Ceiling Fans And Lights. Leaving lights on when no one is in the room is a waste of electricity and will cause your electric bill to increase. Leaving a ceiling fan on all the time, even when no one is in the room, can also cause an increase in your electric bill.
Is it bad to turn your furnace on and off?
When the thermostat detects a decrease in temperature, it switches on the heat circuit and the furnace control board begins the ignition process. … But turning off the furnace in the winter—especially when you’re away for long periods of time—runs the risk of frozen pipes that could easily burst when they thaw.
How much does it cost to replace a limit switch on a furnace?
Average Cost of a New Furnace Limit Switch Depending on who your OEM is, this component could roughly cost you anywhere from $4 to $25.
Why does my furnace run when the heat is off?
So, if your furnace keeps turning off and on too quickly, your thermostat might be malfunctioning or broken. There are several things that could be causing your thermostat to not work properly. The wiring could be old and need replacing, it might need new batteries, or it could be the location of your thermostat.
What does a tripped limit switch look like?
The most common way to tell if a limit switch is tripped is to observe the behavior of your furnace: Your furnace’s heating cycles end right after they begin. If the furnace won’t ignite, but the blower fan stays running, then the high limit switch might be tripped.
How do you reset a furnace after overheating?
- Turn down the thermostat to its lowest setting.
- At the circuit breaker, turn off the power to the furnace.
- If this is a gas furnace, turn off the gas supply at the valve for the main gas pipe, but leave the pilot’s gas supply on.
- If the pilot light was out, light a match to relight it.
