About Furnace Fault Codes

What your furnace's blinking light or error code actually means

What this site is

A reference for furnace and HVAC fault codes across manufacturers. It exists because this information is real, in demand, and almost entirely locked inside PDF service manuals and scattered forum replies. The goal is one clear page per code: what it means, what causes it, what is safe to check, and where the line is between a homeowner fix and a technician call.

How the pages are written

Pages are drafted with AI assistance from manufacturer service literature, published installation manuals, and industry technical references, and every factual claim is checked against a listed source before publication. Fault code meanings are facts and are reproduced as facts; no manufacturer manual text is copied. Codes vary between manufacturers and even between models from the same manufacturer, so every page states which equipment it applies to. No page is published for a code whose meaning could not be verified.

Corrections

If a page is wrong, it should be fixed. Every page lists the sources it was built from so you can check the reasoning yourself rather than taking it on trust.

Coverage

150 codes documented, published 2026-08-03.

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.