How to Check Limit Switch

You can handle how to check limit switch in your furnace with some basic steps. Grab a screwdriver and a multimeter, then turn off the power at the breaker. Locate the switch near the burner, unscrew it, and test for continuity. If you spot damage or feel unsure, call a professional.

Key Takeaways

• Always turn off the power and gas supply before working on your furnace. This ensures your safety while you check the limit switch.
• Use a multimeter to test the limit switch for continuity. A beep or low resistance indicates the switch is functioning properly.
• Regular maintenance, like changing filters and cleaning components, helps prevent limit switch problems and keeps your furnace running efficiently.

Safety Tips and Tools

Power and Gas Shutoff

Before you start working on your furnace, you need to make sure everything is safe. Here’s what you should do:

1. Turn off the pilot light.
2. Shut off the gas supply by closing the valve connected to your furnace.
3. Inspect the gas line and manually close the valve to prevent leaks.

Tip: Always know where your furnace’s power switch and gas shutoff valve are located. If you ever smell gas or suspect a leak, you can act fast and avoid serious problems.

You should also flip the breaker switch to cut off electrical power. This step keeps the furnace from turning on while you’re working. Shutting off both the gas and electricity helps prevent accidents.

• Make sure other gas appliances stay connected when you close the furnace valve.
• Wipe away dust and debris from visible parts to keep moisture from building up.
• Check all gas valves and attachments for signs of leaks.

Tools for Checking Furnace Limit Switch

You don’t need a lot of fancy tools to check your furnace limit switch. Here’s a quick list:

Safety Reminder: Burns, smoke inhalation, and exposure to toxic fumes are common injuries when handling furnace parts. Always wear gloves and work in a well-ventilated area. If you feel unsure at any point, stop and call a professional.

By following these steps and using the right tools, you can safely check your furnace limit switch and avoid unnecessary risks.

How to Check Limit Switch Step by Step

Locate Furnace Limit Switch

You want to know how to check limit switch in your furnace, so the first step is finding it. Most furnace limit switches sit close to the heat exchanger or blower compartment. The exact spot depends on your furnace brand. Here’s a quick table to help you locate the furnace limit switch:

You’ll usually see a small rectangular or round component with two or more wires attached. If you have a gas furnace limit switch, it’s often near the burners. Use a flashlight to spot it inside the access panel.

Tip: Take a moment to look for any dust or debris around the furnace limit switch. Clean it gently before you move on.

Test a Limit Switch with Multimeter

Once you find the furnace limit switch, you need to disconnect the wires before you test the limit switch. Here’s how you do it safely:

1. Turn off the power switch or circuit breaker for the furnace.
2. Locate the furnace limit switch near the heat exchanger.
3. Remove the access panel using a screwdriver or nut driver.
4. Document the wire connections by snapping a photo or jotting them down.
5. Carefully disconnect the wires from the switch terminals.

Now you’re ready to test a limit switch. Grab your multimeter and set it to the continuity setting. This setting usually shows a sound wave or diode symbol. If your multimeter doesn’t have a continuity setting, switch it to measure resistance (look for the Ω symbol).

Check Continuity and Voltage

You want to know how to check limit switch for continuity. Here’s what you do:

1. Touch the multimeter probes to the terminals on the furnace limit switch. It doesn’t matter which probe goes where.
2. At room temperature, the furnace limit switch should be closed. Your multimeter should beep or show a continuous reading. If you use the resistance setting, you should see a low resistance value, close to zero ohms.
3. If you don’t get a beep or see infinite resistance, the switch might be faulty.

Note: Always test the limit switch with the furnace powered off. If you want to test the limit switch during furnace operation, make sure you follow all safety steps and keep your hands clear of moving parts.

Interpret Results

After you test the limit switch, you need to understand what the results mean. Here’s a table to help you figure it out:

If you see continuity, your furnace limit switch is doing its job. If you don’t, or if you spot any damage, you need to replace it. Sometimes, airflow problems or dirty air filters can cause the switch to trip too often. Always check these before you swap out the part.

🛠️ If you’re not sure how to check limit switch or you feel uncomfortable with electrical work, call a professional. They can test the limit switch and fix any problems safely.

Furnace Limit Switch Problems and Maintenance

Common Problems

You might notice furnace limit switch problems if your furnace starts acting up. Here are some signs you should watch for:

• The furnace blower keeps running, but your house stays cold.
• The furnace blows cool air instead of warm air.
• You experience frequent furnace shutdowns or the furnace cycles on and off too often.
• The limit switch goes into lockdown mode after rapid on and off cycles.
• Inconsistent heating makes some rooms warmer than others.

Environmental factors like high or low temperatures, humidity, corrosive substances, and vibrations can also cause furnace limit switch problems. If you see these symptoms, you could be dealing with a furnace issue.

Troubleshooting Tips

You can tackle furnace limit switch problems with a few simple troubleshooting steps. Start with regular maintenance:

• Change filters often to keep airflow steady.
• Clean the limit switch, burners, flame sensors, and blower.
• Clear supply and return vents to avoid pressure problems.
• Lubricate moving parts to reduce wear.
• Schedule annual tune-ups for safety checks.

If your furnace not turning on or you notice inconsistent heating, check for dust or debris around the high limit switch. Regular maintenance helps prevent most furnace limit switch problems.

Tip: Always document your troubleshooting steps. This makes it easier to spot patterns and explain issues to a technician.

When to Call a Professional

Sometimes, furnace limit switch problems need expert help. Call a professional if:

• The blower fan runs nonstop, even when the thermostat is off.
• You smell burning or feel unusual warmth near the furnace.
• Heating feels uneven or the furnace cycles too quickly.
• Your energy bills rise for no clear reason.

Professional replacement costs for a furnace limit switch usually range from $100 to $1,000, with the part itself costing $4 to $25. A typical repair visit averages about $270. If troubleshooting doesn’t solve inconsistent heating or persistent furnace limit switch problems, don’t wait—get help.

You can check your furnace limit switch by turning off power, inspecting wiring, and testing with a multimeter. Always clean parts and replace worn components. Remember, safety comes first. Schedule yearly maintenance and call a professional if you notice problems. Regular care keeps your furnace running smoothly.

FAQ

How often should you check your furnace limit switch?

You want to check the limit switch once a year during your furnace maintenance. Regular checks help you catch problems early.

What if your furnace keeps shutting off?

Try cleaning the air filter and checking for blockages. If the problem continues, you might need to replace the limit switch or call a technician.

Can you replace a furnace limit switch yourself?

• Yes, you can replace it if you feel comfortable with basic tools.
• If you feel unsure, you should call a professional for help.