Like other components in your heating system, the limit switch can malfunction . ... However, when a limit switch starts to go bad, it may not turn off at the end of a cycle; the result is a continuously-running blower. A second problem is common with a limit switch is that won't allow the furnace to operate.
How do I know if my limit switch is bad on my furnace?
Check Your Limit Switch
“If the high limit switch was bad, the furnace should not fire . When the high limit switch trips, the flame/heating element will be shut off and the blower will continue to run to clear the heat. The blower will continue to run until either the system is reset, or the limit switch closes.”
What causes limit switches to go bad?
When your furnace doesn't have proper airflow, like when it is operating with a dirty filter, your heat exchanger will repeatedly overheat and put your limit switch through excess wear and tear. This can eventually cause it to malfunction.
Why does my furnace limit switch keep tripping?
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. ... A dirty filter is the most common cause of airflow issues.
Can a furnace high limit switch go bad?
The Limit Switch Needs Replacement
Over time, high limit switches can wear out and weaken . A faulty high limit switch can trip at lower temperatures, causing short cycling and triggering lockout mode even though the furnace is not actually overheating.
How much does it cost to replace a limit switch on a furnace?
Another safety control is a high limit switch, which measures the temperature of the furnace to ensure it is running within safe temperatures. Both of these are small but critical parts for safe furnace operation, and they will run from $150 to $400 to repair.
How do you test a furnace fan limit switch?
Watch the oil or gas burner: The furnace oil or gas burner should turn ON and subsequently the FAN LIMIT control should turn the burner back OFF when the temperature in the supply air plenum reaches the FAN LIMIT set point. Watch the dial on the fan limit switch moving to confirm its operation.
Can you reset a limit switch?
The function of your furnace limit switch is to tell the fan when to turn off and on depending on the temperature in the home. ... However, for your own safety, don't attempt to reset the switch without first consulting your furnace's instruction manual .
How many limit switches does a furnace have?
Identifying the Limit Switch
The mounting plate usually contains two or more terminals that receive control wires for the blower fan and the furnace's gas valve. It's possible that your furnace will have two or even three limit switches that check temperatures at different parts of the furnace.
Can you bypass a high limit switch?
Yes , you can bypass the high limit switch for testing.
How do you reset a furnace after overheating?
- Turn down the thermostat to its lowest setting.
- At the circuit breaker, turn off the power to the furnace.
- If this is a gas furnace, turn off the gas supply at the valve for the main gas pipe, but leave the pilot's gas supply on.
- If the pilot light was out, light a match to relight it.
Where is the limit switch located on a furnace?
The limit switch is a safety control switch located on the furnace just below the plenum . If the plenum gets too hot, the limit switch shuts off the burner.
How long should a furnace last?
A well-maintained furnace can last at least 15 to 20 years , but completing annual maintenance and being diligent with repairs can extend its life even longer.
How much does it cost to replace a high limit switch?
Relay or High Limit Switch Costs
Relay switches cost $150 to $300 to replace. They might cost $5 to $20 for the part alone with the rest in labor for the trip, diagnosis and replacement. This part allows electricity to flow to the various electrical components inside your unit.
