Modern furnaces offer several tools to make diagnosing problems more straightforward than in the past, but that doesn't mean it's always a simple task to identify an issue. Error codes are one innovation that can help you figure out why your furnace isn't heating your home. In many cases, your furnace will display either a numeric or blinking light code to indicate a problem.

If you have access to your furnace's manual, you can check this code against a table to get an idea of where the problem may lie. However, this approach won't guarantee an accurate or cost-effective fix. For example, what if your furnace shows a problem with the igniter? Running out to buy a new igniter may seem like an easy fix, but it won't always work out as well as you might hope.

Why Aren't Error Codes Fool-Proof?

Automotive mechanics will tell you that the diagnostic error codes that trigger check engine lights are only good as starting points, and the same is true for furnace error codes. Your furnace relies on a relatively simple set of sensors and a basic control board. These components allow the furnace to perform several safety checks and proceed through its normal startup sequence.

However, you can also think of these sensors as the furnaces eyes and ears. It can only report on the things that it can "see" or "hear" with its sensors, and that information may be limited. You'll typically receive an error code indicating an ignition proving fault with ignition. This code simply tells you that the furnace couldn't "see" a flame, so it shut down as a safety precaution.

While one possibility is that you have a faulty igniter, there may also be an issue with the sensor that detects the flame. Since the furnace uses this sensor to detect a flame, it can't tell the difference between a no-ignition condition and a faulty sensor. You may also have other issues, such as a sensor or igniter wiring problem or even low gas pressure.

How Do Professionals Diagnose Problems?

Professional HVAC contractors follow several diagnostic steps to guarantee they aren't throwing money at good parts. While a no-ignition fault code provides a good place to start, an experienced technician will avoid making a diagnosis on that basis alone. Instead, they will check the igniter, sensor, wiring, and anything else that may prevent the furnace control board from detecting successful ignition.

Although this process may seem lengthy to diagnose a relatively simple problem, it's crucial to getting a permanent and reliable fix. Throwing parts at any problem with your HVAC equipment is often costly and may leave you with a furnace that still won't heat your home. If your furnace is throwing an error code and you aren't absolutely sure of the cause, contact a furnace repair professional as soon as possible.