Your furnace is blinking at you.
Here's exactly what it's saying.
Furnace control boards report faults as light patterns and display codes. Generic code tables on the internet are often wrong — different generations of the same brand use different maps. Every code here is tied to its exact series and verified against the manufacturer's service manual, with the source page cited.
Pick your furnace brand
| Brand | Code systems covered | Verification |
|---|---|---|
| Goodman | Single red LED — flash codes · Dual 7-segment display (two-stage variable-speed) · Three-character status display (GMVC96) · GMEC96 tri-color control — red fault flashes · Modulating furnace (GMVM97) — dual 7-segment display | Official service manual |
| Amana | Dual 7-segment display (two-stage variable-speed) | Official service manual |
| Carrier | Status LED — short + long flash codes · Status LED — two-stage variable-speed (58MVP / 58MVB / 58UVB) · Status LED, modulating furnace (59MN7A) | Official service manual |
| Bryant | Status LED — short + long flash codes | Shares Carrier platform |
| Payne | Status LED — short + long flash codes | Shares Carrier platform |
| Rheem | Rheem 801S downflow single-stage control (manual 92-24161-143-14) | Official service manual |
| Trane | Trane S8X1 single-stage furnace control display (2024 IOM) | Official service manual |
| American Standard | American Standard Silver S8X1 furnace control display (2024 IOM) | Official service manual |
| Lennox | Lennox ML193UHE with ignition control 103217-03 | Official service manual |
| York | York TM9E single-stage ECM tri-color LED control | Official service manual |
| Heil | Heil G80CTL Series A amber LED control | Official service manual |
Furnace symptoms
Choose the problem you see below. Each guide starts with checks you can make from outside the furnace and explains when to call for service. If a code is showing, use the brand and model reference to read it.
Or decode the blink pattern directly
Watching a light flash and counting? Use the blink decoder — tell it what you see (three short, one long…) and it matches the code.
New: 2026 U.S. Furnace Fault-Code Search-Demand Snapshot
This snapshot documents 30 candidate furnace fault-code phrases from 2026 U.S. search data and links the strongest demand directly to the fault-code pages we have already verified on this site. Review the data and method →
First: six signs that mean stop troubleshooting
Codes are for furnaces that are failing safely. These are not:
- Gas smell — leave, touch no switches, call your gas utility from outside.
- CO alarm sounding — everyone out, call 911 from outside.
- Headache/nausea that improves when you leave the house — treat as CO. Out, air, 911.
- Flames outside the burner, or scorch marks — power off, technician before next run.
- Burning smell or smoke — breaker off, call for service.
- You've reset a lockout more than twice — stop; each retry can leave unburned gas in the exchanger.
Full emergency guide — what to do and why, for each sign →
Why trust this over a random blog table?
- Every code cites the service manual and page it came from — check our work.
- Codes are bound to their exact model series. Same brand, different generation = different code map (we verified cases where the same flash count means opposite things).
- We tell you when a fix is a $10 DIY part and when it's genuinely a technician's job — including the safety cases where you should stop and call.