Why does limit switch sometimes stay open the flame is out but fan still runs till its cooled down?

A limit switch is a safety device that is used to prevent damage to equipment or injury to personnel in the event of a malfunction or failure. In the case of a furnace, the limit switch is designed to shut off the gas supply if the flame goes out. This is to prevent the build-up of unburned gas in the furnace, which could lead to an explosion.

If the limit switch is not working properly, it may not shut off the gas supply even if the flame goes out. This could lead to a dangerous situation. There are a few reasons why a limit switch might not be working properly, including:

* The limit switch is dirty or damaged. If the limit switch is dirty or damaged, it may not be able to sense the presence of a flame. This can cause the limit switch to stay open even if the flame is out.

* The limit switch is positioned incorrectly. If the limit switch is not positioned correctly, it may not be able to sense the presence of a flame. This can cause the limit switch to stay open even if the flame is out.

* The limit switch is not properly wired. If the limit switch is not properly wired, it may not be able to send a signal to the gas valve. This can cause the limit switch to stay open even if the flame is out.

If you think that your limit switch is not working properly, it is important to have it inspected by a qualified technician. This will help to ensure that your furnace is operating safely and efficiently.

In the meantime, you can take a few simple steps to try to troubleshoot the problem. First, check to make sure that the limit switch is clean and undamaged. If the limit switch is dirty, clean it with a soft cloth. If the limit switch is damaged, it should be replaced.

Next, check to make sure that the limit switch is positioned correctly. The limit switch should be positioned so that it is directly in the path of the flame.

Finally, check to make sure that the limit switch is properly wired. The limit switch should be wired according to the manufacturer's instructions.

If you have tried all of these steps and the limit switch is still not working properly, you should contact a qualified technician.