Can you bypass a limit switch on a furnace?
Yes, you can bypass the high limit switch for testing.
What causes a limit switch to be open?
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. The most common reason for limits to open is a plugged filter or a dirty blower wheel. On the left are some high temperature limits used in furnaces.
How do you test a furnace fan limit switch?
Fan Limit Swith Checkout Procedure
- Disconnect the fan motor circuit at the L4064.
- Turn on power and set thermostat to call for heat.
- Turn off power, recconnect the fan switch, turn on power and again set thermostat to call for heat.
- Fan should come on when plenum temperature has reached fan-on setting.
What will happen if the limit switch opens while the furnace is operating?
The same effect can result from repeated overheating. If a limit switch (doing its job) hits its top limit and has to shut off the burner four or so times, the control computer of the furnace may go into a “hard shutdown” mode so the furnace won’t turn on until the unit is serviced.
Why does my furnace 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 failure?
Airflow issues usually cause a high limit switch to trip out. With less airflow going through your furnace, the heat exchanger excessively heats up and causes the limit switch to trip. Airflow issues can be caused by many different things such as: Dirty air filter.
What causes furnace limit switch trip?
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. Check your air filter, and replace it if dirty.
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 should my furnace limit switch be set at?
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 much does it cost to replace a limit switch on a furnace?
You’ll need to get a limit switch from the same company that makes your furnace. This component could cost anywhere from $4 to $25, depending on your original equipment manufacturer.