How to test and replace a furnace control board

A bad furnace control board can cause all kinds of issues, including keeping your house from staying warm. The good news is that testing and replacing a furnace control board is something you can do yourself with a few simple tools. We’ll show you how to diagnose a faulty control board to get your furnace running smoothly again.

This article provides general guidance and may not correspond precisely to your specific appliance model. While we strive to offer practical tips for a range of DIY appliance repairs, variations in model designs and configurations can result in differing troubleshooting steps, error codes, or replacement parts. For the most accurate information, please refer to the technical sheet or user manual specific to your appliance.

Safety precautions

When working on any appliance, remember to keep safety first. Here are some tips to keep in mind: 

• Always power off and unplug your appliance or switch off the circuit breaker before attempting any maintenance or replacement work. This keeps you safe by preventing any risk of injury from electric shock.
• Wear insulated work gloves to protect your hands from sharp metal parts, pinching hazards and debris.
• Take your time and don’t rush while working to prevent accidents and personal injuries.
• Work in a well-lit area so you can clearly see and access the interior parts.
• Clear your workspace of clutter and other obstacles. Keep children and pets away from the work area.
• Never work on internal parts with bare wet hands. Make sure the work area is completely dry.
• Check your user manual to see if there are specific installation or safety instructions for your part or appliance. 
• Be gentle when handling or removing parts. Excessive force might damage the appliance or cause injury.
• Wear safety glasses when working with chemicals, dust or cleaning large debris to prevent injury. 
• If the appliance has recently been used, give it plenty of time for any heating parts to cool down before working on it. 
• Take pictures or make a note of wiring terminals or other connections before disconnecting to prevent any problems with reassembly.
• When working with wires, avoid touching any exposed wires or terminals. If you need to touch a wire, use a non-conductive tool or wear insulating gloves to prevent electrical shock.

Signs you need to replace the control board

A faulty control board can cause a variety of issues with your furnace. Identifying the problem early can help prevent a complete system failure. Here are the common signs that your furnace control board might need replacing:

• Not starting: If the furnace is receiving power but doesn’t turn on, it could be a sign that the control board is malfunctioning and not sending the right signals to the furnace’s components.
• Erratic behavior: Turning on and off randomly, or going through its heating cycle erratically, could indicate a problem with the control board’s communication with other parts like the blower motor or ignition system.
• Blower motor issues: The blower motor may run continuously or not turn on at all if the control board is not sending the correct signals.
• Error codes or flashing lights: Many modern furnaces display error codes or flashing lights when there’s an issue with the control board. These codes can help pinpoint the problem. Refer to your furnace’s manual for specific error code meanings.
• Failure to ignite (gas furnaces): If the furnace is a gas model and fails to ignite or produce heat, the control board might not be sending the proper signals to the ignition system or gas valve.

If you notice any of these symptoms, the control board could be the cause, and it’s time to test and potentially replace it.

Tools and materials you may need

Before diving into the repair, make sure you have all the necessary tools and materials to complete the job safely and effectively. Here’s what you may need:

• A Phillips or flat-head screwdriver (depending on your furnace) 
• Multimeter 
• Replacement control board. Make sure you purchase a replacement control board that matches the model of your furnace. You can find compatible parts on AppliancePartsPros.com. Double-check the part number and specifications to ensure it fits.
• Camera or notebook to document how the wires are connected to the old control board.  
• Flashlight

How to test the control board

Before replacing the control board, it’s important to test it to confirm that it’s faulty. In many cases, other electrical components may be causing the issue. Here’s how to test the furnace control board with a multimeter:

1. The control board is usually housed within a compartment inside the furnace, and it’s often near the blower motor or burner assembly. 
2. Depending on your furnace model, you may need to use a screwdriver to remove the access panel. The panel is typically secured with screws or clips. 
3. Once removed, you should have access to the inner components of the furnace.
4. In a gas furnace, the control board is typically located near the burner assembly or beside the gas valve. It may be mounted directly onto the metal frame of the furnace.
5. For electric furnaces, the control board is usually found near the blower motor, controlling the fan and the heating elements.
6. The control board will often look like a rectangular circuit board with various wires and connectors attached to it. It might have a series of diagnostic lights or error codes visible on the board.
7. Set your multimeter to measure AC voltage (for most furnace control boards). If you’re testing for continuity, switch it to continuity mode (the multimeter will beep when there’s continuity).
8. Place the multimeter probes on the terminals that are connected to the power supply.
9. Check the voltage reading on your multimeter. You should see a reading close to the furnace’s rated voltage (usually 120V for most systems).
10. If there’s no voltage or a very low reading, the control board may not be receiving power and could be faulty.
11. Visually check the control board for signs of burning, corrosion, or other damage. Sometimes, physical damage to the board is enough to identify the issue.

Replacement steps

Now that you’ve confirmed the control board is faulty or needs replacing, it’s time to remove the old board. Here’s how to safely do it:

1. Before disconnecting anything, take a photo of the wiring or make a note of how the wires are connected to the control board.  
2. Using pliers or a wrench, carefully disconnect the wires attached to the control board terminals. Be gentle, as the terminals may be fragile. If the wires are difficult to remove, make sure you’re not pulling on them too hard.
3. The control board will likely be held in place by screws or clips. Use a screwdriver to remove these fasteners. Be sure to keep track of the screws in case you need them for the new control board.
4. Once the wires are disconnected and the screws are removed, carefully lift the old control board out of the furnace. Be mindful of any other parts around the board, and ensure you don’t damage any surrounding parts.
5. Place the new control board in the same position as the old one. Ensure that the mounting holes line up with the ones on the furnace frame.
6. Use the screws you removed earlier to secure the new control board in place. Tighten the screws, but don’t over-tighten, as this could damage the board or the mounting holes.
7. Refer to the photo or notes you took earlier to reconnect the wires to the correct terminals on the new control board. Double-check the connections to make sure they are secure and correctly placed.
8. Once the board is securely installed and all wires are connected, do a quick visual inspection. Make sure there are no loose connections, exposed wires, or other potential issues.
9. Carefully align and replace the furnace access panel that you removed earlier. Secure it with screws or clips to make sure it’s properly sealed.
10. Flip the power switch back to the “On” position, or reset the circuit breaker to restore power to the furnace.
11. Adjust the thermostat to a higher temperature to trigger the furnace to start up. This should prompt the system to go through its heating cycle, starting with the ignition (for gas furnaces) or heating elements (for electric furnaces).

Need more help?

Thanks for reading! If you’re searching for replacement parts, grab your model number and visit AppliancePartsPros.com. We have over two million parts in stock, and most ship quickly, arriving in just two business days. Need assistance? Call our team anytime at 1 (877) 477-7278.

In the meantime, take a look at our DIY blog or watch our extensive library of video tutorials on our YouTube channel.

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