Today's furnaces are more efficient and often better made than those from years past. However, they do still include a lot of moving parts and pieces, and sometimes one of those parts or pieces fails. One of the most common parts of a furnace to fail is the limit switch, sometimes known as the high-temperature limit switch. It's a good idea to know the signs of a broken limit switch and to be familiar with how HVAC repair teams address this problem.

Role of the Limit Switch

To understand the signs of a failed limit switch, you first need to understand this part's role in the furnace's operation. After your furnace stops heating, the fan keeps blowing for a while. This ensures all of the heat from the furnace gets blown into your home. The limit switch detects when the furnace burner is cool and turns off the fan. Later, when the furnace turns back on, the limit switch senses that the furnace is heating up and turns the fan back on.

Signs of a Failed Limit Switch

The signs of a failed limit switch depend on whether the switch is stuck in the "on" or "off" position. If it is stuck on, the furnace will generally keep blowing long after it stops generating heat. The fan may not kick off at all until you turn it off manually. If the switch is stuck off, then the furnace generally won't turn on, no matter how high you turn the thermostat setting.

Fixing a Broken Limit Switch

If your limit switch breaks, an HVAC contractor will generally remove the old limit switch and put a new one in place. You may have to wait a day or two for this repair, simply because each furnace model requires a different type of limit switch. If your HVAC contractor does not have one for your unit in stock, they may have to go buy one from a supplier. 

Limit switches are rather inexpensive and only take a few minutes for a good HVAC contractor to replace. So, this is rarely a reason to replace your whole furnace. However, if your furnace has other problems, such as worn bearings or a torn belt, the repair bills will be higher, and it may, in fact, be in your best interest to replace the furnace instead of repairing it.

If your limit switch fails, call an HVAC contractor. They'll handle things from there. 

For more info about heating systems, contact a local professional.