Why does my high 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.

Why does my furnace high limit switch keep tripping?

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. Clean and replace dirty and worn-out parts to fix the problem.

What causes limit switch problems?

These problems are most commonly brought on by airflow issues in your system. When your furnace doesn’t have proper airflow, like when it is operating with a dirty filter, your heat exchanger will repeatedly overheat and put your limit switch through excess wear and tear. This can eventually cause it to malfunction.

How do I know if my 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 do you bypass a limit switch?

1. Locate the Limit Switch in the Furnace.
2. Remove the two wires going to the Limit Switch.
3. Insert a shielded jumper wire in-between the two wires.
4. Once jumpered, test the furnace; if it works, the switch is bad and needs to be replaced.

Is a high limit switch normally open?

Limit switch information page. 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.

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.

What does open high limit mean on a furnace?

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. Limit switches turn off the burner and turn on the circulating fan if there is a high temperature condition in the furnace. Play. Pause.

Do furnace rollout switches go bad?

Sometimes, your furnace’s flame rollout switch might go bad. What is this? For instance, if your flames are not rolling out, but the rollout switch is tripping, then the rollout switch might be bad. Normally, a flame rollout switch will close when it’s not tripped.

How does a high limit thermostat work?

Anytime you have an element that heats, safety dictates you have a way to stop the appliance from overheating in case the temperature-regulating controls fail. That’s what the high-limit thermostat does: It shuts off the heating element if the water reaches an upper temperature limit, usually about 200 degrees.

Article first time published on

What causes roll out switch to trip?

Rollout switches trip because flames are burning back where they are not supposed to be. Possible causes include a stopped up vent, a stopped up heat exchanger, low gas pressure, or a cracked heat exchanger. … A cracked heat exchanger can also lead to tripped rollout switches.

What does a rollout limit switch do?

Rollout switches are typically going to be a manual reset switch with a higher temperature rating than the other limits within the unit. This is because the purpose of the rollout switch is to detect overheating or even a possible flame rollout, which can occur if there is a crack in the heat exchanger.

Why does high limit thermostat go bad?

Blown Thermal Fuse A frayed wire can cause a thermostat to keep going bad. A dryer will blow a thermal fuse if it’s close to overheating. Each time the thermal fuse blows it can interfere with a thermostat’s function and cause it to go bad, too.

How do I know if my cycling thermostat is bad?

1. The drum spins, but the air inside does not heat up.
2. Your dryer will sound like it’s working, but when it stops, your clothes are still wet.