How to troubleshoot and replace a furnace pressure switch

If your furnace isn’t running quite right, a pressure switch could be the culprit. This little part is responsible for making sure your furnace gets the right amount of air pressure to run safely. When it malfunctions, you might notice that the furnace won’t start or keeps turning off unexpectedly.

The good news is, a lot of pressure switch issues are easy to fix yourself. We’ll walk you through how to troubleshoot and replace a faulty pressure switch without needing a professional. So, let’s dive in and get that furnace back to working like it should.

The tips in this article might not fit your exact appliance model. We aim to provide useful advice for all sorts of DIY appliance fixes, but different models can have unique troubleshooting steps, error codes, parts, etc. To get the most precise guidance, we highly suggest checking your appliance’s manufacturer documentation, finding your model number here, or reaching out to us if you have any questions.

Safety precautions

Safety comes first when working on any appliance. Here are some practical tips to help keep you safe:

• Always turn off the power by unplugging the appliance or switching off the circuit breaker before starting. This protects you from the risk of electric shock.
• Wear insulated gloves to protect your hands from sharp edges, pinching hazards, or debris.
• Take your time and work at a steady pace to avoid accidents or injuries.
• Make sure your workspace is well-lit so you can clearly see and access the parts you’re working on.
• Keep your area organized and free of clutter, and ensure children and pets are kept away from the workspace.
• Never handle internal parts with wet hands. Make sure both your hands and the work area are completely dry.
• Check your appliance’s user manual for specific instructions or safety guidelines related to your repair.
• Handle parts gently to prevent damaging the appliance or injuring yourself by using too much force.
• Wear safety glasses if you’re dealing with chemicals, dust, or large debris to protect your eyes.
• If the appliance was recently used, give it time to cool down before working on any heated components.
• Take photos or notes of wiring connections before disconnecting anything. This makes reassembly much easier.
• Avoid touching exposed wires or terminals. If you need to handle wires, use non-conductive tools or wear insulated gloves to reduce the risk of electrical shock.

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1. Inspect the pressure switch tubing

The tubing connected to the pressure switch plays a key role in ensuring the switch gets the right air pressure reading. If there’s any issue with the tubing, such as cracks, blockages, or loose connections, it could cause the pressure switch to malfunction.

How to inspect the tubing:

1. Find the rubber tubing connected to the pressure switch. It is usually attached to the draft inducer motor. Refer to your furnace manual if you’re having trouble locating it.
2. Look closely for any visible cracks, tears, or signs of wear in the tubing.
3. Check for any blockages inside the tubing that could be obstructing airflow. You might see debris or dirt build-up that could prevent proper pressure sensing.
4. If the tubing is cracked or damaged, replace it with new tubing.
5. If there’s a blockage, you can use compressed air or a thin wire to clear it out. Be careful not to damage the tubing while doing this.
6. Make sure the connections are secure. If they’re loose, tighten them to make sure the tubing stays in place.

2. Test the pressure switch 

Now that you’ve inspected the tubing, it’s time to test the pressure switch itself. The pressure switch works by detecting whether the furnace is creating the correct air pressure. If it’s faulty, it can prevent the furnace from operating properly.

How to test the pressure switch:

1. Set your multimeter to measure continuity (the lowest setting, usually represented by a symbol like a soundwave or diode symbol).
2. Make sure you have the correct probes and settings for testing electrical parts.
3. Disconnect the wires from the terminals of the pressure switch. Make sure to take note of where the wires are connected (taking a picture or writing it down can help you during reinstallation).
4. Attach the multimeter probes to the terminals of the pressure switch.
5. If the furnace is running and the switch is working, you should hear a click and see continuity on the multimeter display.
6. If there’s no continuity when the switch is activated, the pressure switch may be faulty and needs replacing.

If your test shows no continuity, the pressure switch is likely malfunctioning. It’s time to replace it.

3. Check the draft inducer motor

The draft inducer motor creates the airflow needed for the pressure switch to work. If the inducer motor is not working properly, it can affect the air pressure reading and prevent the furnace from starting or running.

How to check the inducer motor:

1. The inducer motor is typically located near the burner assembly. Check your furnace manual for the exact location.
2. Look for any visible signs of wear, rust, or damage on the motor. Make sure it is securely attached to the furnace and free from debris or dirt buildup.
3. Turn on the furnace and listen for the inducer motor to start. If it doesn’t run, or the airflow seems weak, the motor may be faulty.
4. Use a multimeter to test the motor for continuity. Set the multimeter to measure resistance (ohms) and place the probes on the motor’s terminals. If the multimeter shows no continuity, the motor needs to be replaced.
5. If the motor is dirty, clean it carefully with a soft brush or vacuum. Remove any debris that might be blocking the airflow.

If the motor is faulty or not working correctly, it will need to be replaced. Make sure that you install the correct replacement motor for your furnace model.

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4. Check the furnace vent 

A blocked vent can prevent the proper airflow needed for the pressure switch to register, which could be why your furnace isn’t functioning correctly. Checking that the vent is clear of obstructions is an important step in troubleshooting furnace issues.

How to check the furnace vent:

1. Find the vent that leads from the furnace to the outside of your home. This is usually connected to the draft inducer motor or exhaust system.
2. Look for any visible blockages like leaves, debris, ice, or bird nests that could be obstructing the vent. These blockages can disrupt airflow and affect furnace operation.
3. Check both the exterior vent and the interior portion connected to the furnace.
4. If you find a blockage, clear it using a long brush or vacuum to remove debris.
5. If you notice ice buildup (especially during winter months), use warm water or a hairdryer to melt the ice carefully. Never use a sharp object to scrape ice away as it could damage the vent.
6. After clearing the vent, double-check that the airflow is unobstructed, and air can flow freely. This will help the pressure switch function correctly and prevent further issues.

5. Replace the pressure switch if needed

If you’ve checked the tubing, tested the switch, inspected the inducer motor and vent, and the problem persists, it might be time to replace the pressure switch. This part can wear out over time, especially if the furnace has been running inefficiently or experiencing other issues.

How to replace the pressure switch:

1. For safety, always make sure the furnace is completely off and the gas supply is shut off before performing any repairs.
2. Disconnect the wiring from the faulty pressure switch. Take note of how the wires are connected, as you’ll need to reconnect them to the new switch later.
3. Use a wrench or screwdriver to remove any screws or bolts securing the pressure switch in place.
4. Once detached, carefully remove the old pressure switch.
5. Take the new pressure switch and align it in the same position as the old one.
6. Secure the switch in place with the screws or bolts.
7. Reconnect the tubing and wiring as it was before, making sure everything is tightened and secured.

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Additional help

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