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Heil furnace codes

How to Troubleshoot Heil Furnace Codes Quickly

Do you want to know how to troubleshoot Heil furnace codes easily? Heil furnaces, renowned for their reliability and efficiency, have garnered a solid reputation in the HVAC industry. Like…

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Do you want to know how to troubleshoot Heil furnace codes easily?

Heil furnaces, renowned for their reliability and efficiency, have garnered a solid reputation in the HVAC industry. Like all appliances, they can sometimes experience technical difficulties or malfunctions. 

When this happens, the key to troubleshooting lies in understanding the error codes displayed on the furnace’s control board. These codes help in identifying the root cause of the issue, guiding you on how to address it effectively.

In this comprehensive guide, we will delve into some of the most common Heil furnace codes, their meanings, and how you can troubleshoot them.

What are Heil Furnace Codes?

Before we get into the nitty-gritty, it’s important to establish what Heil furnace codes are. Essentially, these codes are alphanumeric sequences displayed on the control board’s LED display. This control board is usually situated inside the furnace cabinet or on the blower compartment door. Depending on the situation, these codes can flash at different intervals, representing normal operation or signaling potential issues.

For instance, a code that flashes on and off twice, pauses for two seconds, and then repeats indicates a specific issue. On the other hand, a rapid flash is usually reserved for factory testing and indicates an error.

Understanding these codes is the first step towards troubleshooting your Heil furnace and keeping it running smoothly.

READ: How To Fix The Common Amana Furnace Fault Codes

Decoding Heil Furnace Codes

To effectively interpret Heil furnace codes, it’s essential to focus on the number of flashes displayed on the LED. Each flash count represents a different issue. Here is a table that breaks down what each flash count means:

Flash CountCode Description
One flashSystem lockout (retry or recycle failure)
Two flashesSystem lockout (hard lockout)
Three flashesPressure switch open
Four flashesHigh limit switch open
Five flashesFlame sensed when no flame should be present
Six flashesPressure switch did not close or reopened
Seven flashesLow flame sense signal
Eight flashesInternal control fault
Nine flashesPolarity reversed
A table showing Heil furnace codes

In-depth Troubleshooting of Heil Furnace Codes

Upon identifying the number of flashes and the corresponding code, you can delve into troubleshooting. Whether you can address the issue yourself or require professional assistance depends on the severity and type of the code. Here are in-depth potential solutions for each code:

One flash: System lockout (retry or recycle failure)

This code is indicative of an automatic reset failure. The first line of action is to reset the furnace. To do this, turn off the power for about a minute and then turn it back on. If the issue persists, it could signify a defective control board or a significant system issue. In such a case, it would be prudent to seek professional help to avoid exacerbating the problem.

Two flashes: System lockout (hard lockout)

This code suggests a more serious system issue, such as a repeated failure that has led to the system shutting down. It could point to a fault in the main controller board, improper calibration, or a major mechanical failure. Because this code signifies a complex issue, it is recommended to consult with a professional technician to diagnose and fix the problem.

Three flashes: Pressure switch open

When the pressure switch is open, it interrupts the circuit and the furnace cannot operate. This could be caused by a blocked vent pipe or air intake pipe that’s reducing the airflow and preventing the pressure switch from closing. Alternatively, a cracked or clogged pressure switch hose might be to blame. Check these areas and clear any obstructions, replace the hose if it’s damaged, and check if the pressure switch itself is faulty.

Four flashes: High limit switch open

This code indicates that the furnace is overheating, which can be caused by a dirty or clogged air filter, improper duct sizing, a faulty blower motor, or restricted circulating airflow. Therefore, your response should include replacing or cleaning the air filter, checking the duct size to match your furnace’s capacity, and checking for obstructions in the airflow.

Five flashes: Flame sensed when no flame should be present

This code suggests that the control board is detecting a flame when there should be none, hinting at a gas valve leakage. This is a hazardous situation that necessitates immediate professional assistance. Do not attempt to solve this issue by yourself as it could lead to a gas leak or a potential fire hazard.

Six flashes: Pressure switch did not close or reopened

This problem could be caused by incorrect pressure switch wiring, a faulty pressure switch, or a malfunctioning inducer motor. Examine the wiring of the pressure switch and replace the switch if necessary. The inducer motor should also be tested to ensure it’s working properly.

Seven flashes: Low flame sense signal

This code could indicate an issue with the flame sensor. Dirt build-up or a faulty sensor could be causing the problem. Try cleaning the flame sensor with a non-abrasive cleaner. If the problem persists, consider replacing the flame sensor.

Eight flashes: Internal control fault

This code indicates a malfunction within the control board itself, potentially due to a faulty thermostat connection or a power supply issue. You might need to replace the control board if it’s defective.

Nine flashes: Polarity reversed

This suggests that the power supply has reversed polarity, which could be due to improper electrical wiring. Check the electrical wiring against the schematic, and if you’re uncertain, call a certified electrician to prevent the risk of electric shock.

READ: Payne Furnace Codes: What You Need To Know


Heil furnace codes serve as a powerful diagnostic tool that can help troubleshoot your furnace and ensure its smooth operation. However, if you are not comfortable or confident in performing any of the repairs yourself, always get professional help. Always follow safety precautions and turn off the power supply before working on your furnace.

We hope this comprehensive guide has provided you with the necessary knowledge to troubleshoot Heil furnace codes effectively.

I'm an HVAC enthusiast and a passionate writer dedicated to sharing valuable insights and practical tips about heating, cooling, ventilation, and air conditioning systems.

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Hi there, I'm Robert Brooks

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