Why Is Your Furnace's Limit Switch Tripping?

The limit switch in a furnace does a couple of useful jobs. It helps control the temperature of your air flow. It also helps prevent damage to the furnace and accidents in your home by shutting the system down if it overheats.

Sometimes, limit switches start to trip too often or fail to work correctly. Why does this happen?

Your Furnace Overheats

Limit switches can start to cycle on and off too frequently if your furnace overheats and doesn't cool down to the right temperature. This can be caused by problems with internal parts such as a fan or filter.

For example, if your fan is faulty, then it won't control the temperature in your system. Or, if you haven't changed your filter recently, then it might have reached the end of its working life. A clogged filter won't allow air to flow through it, so your furnace might overheat.

When this happens, your limit switch might shut the furnace down repeatedly to try to get it down to an acceptable temperature. Sometimes, repetitive on/off cycling makes the switch move into a safety lockout mode.

Here, the switch thinks that your furnace has a serious problem when it doesn't. It will shut the furnace down so that you can't use it.

If your filter makes your furnace overheat, then installing a new one should fix the problem. Fans might need a repair. If your furnace is in lockout mode, then a furnace repair specialist can check your system, make any necessary repairs, and reset your furnace.

Your Switch Is Broken

Like any working furnace part, limit switches can wear down or simply break over time. They can lose some of their connections. So, a switch might start working erratically. Or, it might not work correctly.

A faulty switch that still works might trip at a lower temperature than it should. You might not get enough heat in your home because the switch won't allow the furnace to reach its optimum heat capacity.

Sometimes, switches fail because other parts have problems. For example, if your furnace constantly overheats because of a filter or fan problem, then your switch will be exposed to too much heat too often. It will trip more frequently which makes it wear faster than it should.

In some cases, a faulty switch will fail to turn off your furnace when it should. Your furnace will stay on all the time. This is a more urgent problem that could cause more serious internal damage. It could also compromise your safety.

To get your furnace working normally again, contact local furnace repair companies.