Any relatively modern furnace will include an electronic control board that manages numerous aspects of the furnace's operation. This board runs through the startup sequence for the furnace, checking each safety switch in order and ensuring your system is running correctly and safely. As an added benefit, these boards can typically display error codes to help troubleshoot many problems.

While furnace error codes are often a sign of an underlying parts failure, they're sometimes the result of poor maintenance. Unfortunately, continuing to defer maintenance for too long will lead to failures and damage. Ignoring the importance of maintaining these three essential furnace items will inevitably result in error codes and a furnace that refuses to operate.

1. Clogged Air Filters

Your furnace's air filter is simultaneously one of the easiest and cheapest items to maintain while also being a source of potentially severe damage. Your furnace requires a constant supply of fresh air across its heat exchanger while the burners are running. This air both heats your home and cools your furnace's heat exchanger. Unfortunately, a clogged furnace filter can drastically restrict airflow.

Without sufficient airflow, your heat exchanger will overheat and can potentially crack. Modern furnaces contain limit switches to detect overheating conditions. When the limit switch triggers, the furnace will typically shut down and display an error code. Allowing this to happen continuously can damage your furnace, so it's crucial to stay on top of filter changes.

2. Overfilled Condensate Lines

Modern, high-efficiency condensing furnaces produce a significant amount of condensate from their exhaust stream. Since these furnaces can extract so much heat from the exhaust gases, the temperature of the stream drops, and water and other chemicals will condense into a liquid. As a result, any furnace must deal with a steady flow of condensate while it runs.

Checking and cleaning the condensate line is an important maintenance item. These lines can become clogged due to dirt and debris, preventing condensate from draining successfully. Once the condensate line reaches a certain point, it will trigger a safety that will shut down the furnace and cause an error code.

3. Dirty Flame Rods

All modern furnaces use flame rods as part of the flame rectification process. This safety device detects heat from the furnace's burners, proving successful ignition to the control board. Without flame rectification, failed ignition could potentially result in a severe gas leak as the burners continue to spew unburnt gas into the combustion chamber.

While flame rods rarely fail, they can accumulate soot and debris that will act as insulators. If the rod becomes dirty enough, it will no longer detect the flame, and your furnace may display an ignition proving error code before shutting down. Inspecting and cleaning the flame rod as part of a regular professional maintenance visit will ensure this fault doesn't leave you in the cold.

Call an HVAC professional if you need furnace maintenance.