Furnace Troubleshooting & Error Codes
Gas furnaces report faults by flashing a status code on a small LED behind the burner door. These pages explain what the manufacturer's own documentation says that code means — and, just as important, where the documentation stops letting a homeowner go.
How these pages are sourced
Every code meaning on this site comes from the manufacturer's published installation instructions, service literature or owner's manual, cited by document number and page. Where a manufacturer's own documents disagree between furnace generations, both readings are given rather than averaged into one answer. No forum, video or repair-shop blog is used as a source for a code meaning.
Safety guidance that is not manufacturer-specific comes from the U.S. Consumer Product Safety Commission. We do not publish a repair procedure that the manufacturer reserves for trained service personnel, which on a gas furnace is nearly all of them.