A furnace uses a number of components to heat up the inside of a home. Each component has a role to play. When one fails, the entire heating system suffers. Today Absolute P&M Services would like to focus on the furnace’s high limit switch. Today we will share what the high limit switch does, it’s failing symptoms, and repair needs.
Function of High Limit Switch
The high limit switch is a small component of a gas furnace and even though it may be small, it has an important job. The high limit switch is essential in the operation of the furnace. The main job of the high limit switch is to activate and deactivate the fan motor. However, the high limit switch also acts as the furnace’s safety device. If the furnace begins to overheat, the high limit switch will turn off the furnace. The high limit switch consists of a temperature sensing probe which detects the furnace’s temperature and react if it begins to overheat. If the high limit switch malfunctions or wears out, the furnace safety device is compromised and the fan motor will not activate.
Signs High Limit Switch Needs to Be Replaced
Just like any other component of the furnace, the high limit switch can wear down and go bad or weaken over time. When the high limit switch goes bad it will not be able to signal the fan motor to switch on or off. In most cases, the high limit switch goes out after a cycle has been triggered. Therefore, the fan motor will continue to run. If the fan motor runs continuously, then most likely the high limit switch will need to be replaced. However, make sure the thermostat setting is on “auto” and not “on”. If the thermostat is on the “on” setting then the motor will continue to run. When the high limit switch begins to wear out and weakens overt time, the high limit switch weakens. It will not activate at the right temperatures. Often it takes the temperature to significantly drop before the high limit switch will activate. If the home gets really cold before the furnace cycle is activated then the high limit switch is wearing down. Another byproduct of the high limit switch wearing down is that the furnace will tend to run longer than normal as the home temperature has dropped too much. If the high limit switch is showing signs of wear it will need to be replaced.
Change Air Filters & Schedule Regular Heating Tune Ups
One of the common reasons why a high limit switch will require premature replacement is because the furnace keeps on overheating. A furnace will most often overheat due to clogged and dirty air filters, and secondly due to poor furnace maintenance. When a furnace is properly maintained and the air filters are not changed out on time, the furnace will work more often and harder which puts additional stress of the high limit switch. To extend the life of the high limit switch, make sure to change out filters and have the furnace maintained.