A bad high limit switch would cause this. The furnace is trying to purge the heat that it thinks is there. Normally the limit switch will reset when the temperature drops. A bad switch will remain open, so the blower will run continuously.

Why is my furnace blower constantly running?

If your fan limit switch is set to AUTO but the fan continues to run without ever stopping, you’ll need to call a professional. Two problems that could cause your fan to run without stopping include: A bad fan limit switch that needs to be replaced. Bad thermostat wiring.

Does the fan in a furnace continue to run if the high limit control opens?

The Fan switch “makes” or closes to permit the fan to run when temperature rises to the FAN ON setting. The High Limit switch “breaks” or opens to turn the burner off if the plenum temperature reaches the high limit setting.

Why does my blower fan keep running?

Faulty Thermostat: If both the fan and either the cooling or heating system are running unexpectedly, you may have a faulty thermostat. Broken Relay Switch or Short Circuit: If only the fan is running, there may be a broken relay switch preventing the settings you enter on the thermostat from being sent to the fan.

Why is furnace fan running non stop?

The fan limit switch is on the wrong mode

Now, if the furnace fan won’t stop running, it may be that either your limit switch has been set to manual override, or the switch itself is faulty and needs to be replaced. Your fan limit switch can be found right under the furnace hood.

Why is my furnace not shutting off?

On your thermostat, look for the fan settings. There should be two, “ON” and “AUTO.” If it seems like your furnace won’t turn off, the thermostat may be set to “ON” for the blower. Toggle the switch to “AUTO” so your furnace’s blower fan only runs during a heat cycle.

Why will a blower run on the on position and not on auto?

That’s because if the heater never warms up then the fan controller won’t automagically turn on the blower fan. Let me know what you find. Electric split unit trane the fan comes on in the on position but not in automatic. Heat or cool isn’t working on the condenser or evaporator .

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.

Can a furnace 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.

How do you reset a limit switch?

How to Reset a Furnace Limit Switch

  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.

How do you reset the limit switch on a furnace?

You can try resetting the furnace limit switch yourself if you have a newer model by turning off the furnace for 30 seconds and then turning it back on. However, if this does not work or the furnace repeatedly shuts down, calling heating experts to reverse or reset the limit switch is a good idea.

What happens when high limit switch trips?

If the furnace high limit switch is tripping, it will wear out at some point. Eventually, it will trigger a lockout mode, and your gas furnace will be unable to operate until the switch is reset or replaced. Make sure you contact your technician to perform this repair task.

How does a furnace high limit switch work?

Also known as the fan limit switch or simply the limit switch, it has two functions in the furnace’s operation: It turns the fan on and off during the normal heating cycles of the furnace, and it senses heat and shuts down the furnace if the interior temperature gets too high.

Can you bypass a high limit switch on a furnace?

Yes, you can bypass the high limit switch for testing.

What causes high limit switch open?

The high temperature limit switch (also known as a furnace plenum thermostat) is a safety device on a furnace that is designed to cut the gas supply when the burner temperature exceeds the safe operating range. When the temperature drops back within the safe range, it will allow the gas valve to open again.

Is a high limit switch normally open?

The fan limit switch is normally open and closes when the temperature reaches its preset value, whereas the high limit switch is normally closed and opens when the temperature reaches its threshold value.

How do you troubleshoot a limit switch?

Quote from the video:
Quote from Youtube video: And you can simply take a resistance. Reading across the limit. Go on lead on each of the terminals. And if the limit switch is closed you should have reading of zero.