What is a high limit switch on a furnace

What Is a Furnace Limit Switch? The high limit switch is a furnace component that controls elements of operation and safeguards the system. This component is connected to the blower motor as well as the gas valve and consists of a probe that detects temperatures mounted to a metal plate.

How do I know if my limit switch is bad on my furnace?

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 do you know if a limit switch is bad?

Limit Switch Malfunctions One common symptom of a malfunctioning limit switch is a blower fan that doesn’t shut off. This happens when the switch fails to shut off after the burners have stopped and the air exchanger is sufficiently cool. A bad switch also can prevent a furnace from operating at all.

How do you reset a high limit switch on a furnace?

  1. Locate your furnace’s heating duct. …
  2. Locate the white limit switch. …
  3. Look at each arm to identify the settings. …
  4. Identify the component (setting) located in between the two arms. …
  5. Set the temperature on the middle component to approximately 105 to 115 degrees Fahrenheit.

What trips a high limit switch?

A high limit switch will keep tripping due to a dirty flame sensor, short cycling, obstructed airflow, or a defective switch. These lead to overheating within the gas furnace that triggers tripping as a safety measure to prevent fires.

How much does it cost to replace a limit switch on a furnace?

Relay or High Limit Switch Costs Relay switches cost $150 to $300 to replace. They might cost $5 to $20 for the part alone with the rest in labor for the trip, diagnosis and replacement.

Can a high limit switch go bad?

Like any other part in your HVAC system, the high limit switch can wear out over time. One of the most common issues that happens when a high limit switch goes bad is that it fails to signal the blower fan to turn off. … High limit switches can also weaken over time so that they begin tripping at a lower temperature.

How does a furnace limit switch work?

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 does a limit switch do?

The limit switch on your air conditioning system is the link between the blower on your air handler and the thermostat. When the thermostat senses that the desired indoor temperature has been reached, it stops the air conditioner from producing any more cold air. … That’s exactly what the limit switch does.

What does open high limit switch mean?

If the furnace failure code indicates an “open limit” or “open high temperature switch” or “open rollout switch”, it is probable that the furnace has overheated. … The limit switch shuts off the burner when the temperature exceeds a preset temperature. When the temperature reduces to normal, the burner will come back on.

Article first time published on askingthelot.com/what-is-a-high-limit-switch-on-a-furnace/

What causes high limit furnace trip?

The limit might trip after start-up due to a restrictive or dirty air filter. Some high performance air filters do not allow very much airflow through them and will cause a furnace to overheat due to a lack of air going across the heat exchanger. Another reason could be a bypass humidifier.

What causes a furnace to go out on high limit?

Dirty air filters are a common cause of furnace cycling problems. Air filters trap dust, dirt and debris. With time, the filter becomes clogged and restricts airflow to the equipment’s heat exchanger. When this happens, the heat exchanger overheats, forcing the high-limit switch to trip and the furnace to cycle off.

Can you repair a furnace limit switch?

Yes, it’s possible to replace a furnace limit switch yourself. To do it, you’ll first need to use a multimeter to test the switch. If it’s faulty, you’ll also need a new switch that matches your old one. … Shut off the power and gas to your furnace.

Can you clean a limit switch?

Remove the high limit switch by removing the two screws that hold it to the plenum. If the flame sensor rod is dirty, you can try cleaning it gently with steel wool or sandpaper, or replace the part with an identical new part.

Should a furnace limit switch be open or closed?

The fan limit switch should be open when the furnace is off and full of cool air, so you should get an OL reading; if not, there’s a short, and the switch should be replaced. The high limit switch should be closed when the furnace is cold, so you should get a zero reading; if you get the opposite, replace the switch.