How to identify and solve blinking light codes on a furnace

As winter settles in, keeping your furnace in tip-top shape is a must to keep your home warm and cozy. But what do you do when your furnace starts flashing lights or error codes at you? It might seem a bit overwhelming, but decoding these blinking lights isn’t as tricky as it seems. With the right know-how, you can figure out what your furnace is trying to tell you and get things back on track.

The info in this article might not match your exact appliance model. While we aim to provide handy advice for all sorts of DIY appliance fixes, different models and setups can mean variations in troubleshooting steps, error codes, parts, and so on. For the most spot-on guidance, we recommend checking the manufacturer’s documentation for your specific model or feel free to reach out to us with any questions.

What those blinking lights mean

When your furnace starts flashing a light code, think of it as its way of sending an error signal. These codes are designed to help you pinpoint and troubleshoot specific issues. Each blinking pattern corresponds to a particular issue, and by decoding them, you can take the steps needed to sort things out.

Read more: 12 simple space heater safety tips for this winter

Common furnace error codes

1 flash: ignition trouble

A single flash indicates an ignition error or flame failure. This could be due to a dirty or faulty flame sensor, a malfunctioning igniter, or an interruption in the gas supply. The flame sensor’s job is to detect the presence of a flame, and if it’s dirty or bad, it might not register the flame correctly.

2 flashes: pressure switch error (stuck closed)

Two flashes point to a pressure switch error where the switch is stuck closed. This might be caused by a short in the pressure switch circuit, a faulty pressure switch, or issues with the draft inducer. The pressure switch makes sure your furnace’s combustion process is safe, so it’s important to tackle this issue promptly.

3 flashes: pressure switch error (stuck open)

Three flashes mean the pressure switch is stuck open. This can happen due to blockages in the pressure switch hose, loose or improper hose connections, or wiring issues. Any blockage or disconnection can stop the switch from doing its job right.

4 flashes: open high limit

Four flashes indicate an open high limit, which could be caused by dirty air filters, wiring problems, or blockages in the flue. The high-limit switch prevents the furnace from overheating, so if it’s open, it might be a sign that things are running too hot.

Read more: Your guide to choosing a space heater

Safety first

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.

Read more: 12 things you should know about portable space heaters

Troubleshooting and fixing blinking light codes

Step 1: watch the blinking pattern

First, take a good look at the blinking pattern of the furnace light. Count how many times it flashes and note any pauses between them. This sequence is key to decoding the exact error your furnace is experiencing.

Step 2: check your furnace manual

With the blinking pattern noted, grab your furnace’s installation guide or manufacturer documentation. This guide will have a list of error codes specific to your furnace model. If you can’t find the manual, you might be able to locate it online on the manufacturer’s website, or visit our repair help section for assistance.

Step 3: do some basic checks

Make sure all connections are snug. Loose wires or connections can throw false error codes. Double-check the thermostat settings to ensure it’s set correctly. Sometimes, simple things like a misconfigured thermostat can make the furnace act up.

Step 4: troubleshoot common problems

• For ignition errors (1 flash): Take a look at the flame sensor. If it’s dirty, gently clean it. Check the igniter for any cracks or damage, and make sure the gas supply is steady.
• For pressure switch errors (2 or 3 flashes): Start by inspecting the pressure switch hose for any blockages or disconnections. Ensure the hose connections are tight and debris-free. Check the wiring connected to the pressure switch for any loose connections or damage. If you have a multimeter, you can test the pressure switch according to the manufacturer’s specs to see if it’s working properly.
• For open high limit (4 flashes): Replace dirty air filters to boost airflow. Look for blockages in the flue and make sure all vents are open and clear. Inspect the wiring connected to the high limit switch for any signs of wear or damage.

If you need replacement parts, you can visit AppliancePartsPros.com or learn how to find your appliance’s model number to make sure you find the right part.

Additional information

For all your furnace repair needs and expert advice, head over to AppliancePartsPros.com. We’re here to help you find the right parts and offer the guidance you need for a successful DIY fix.

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