Every modern gas furnace control runs the same bargain: it will retry a failed ignition a few times, because a gust of wind down the vent or a lazy flame signal should not leave you cold. But retries are not infinite. When the failures repeat past the board’s limit, it locks out — burners off, sometimes the blower still running — until a timer expires or power is cycled.
The reset clocks, from the manuals
| Brand / board | Lockout behavior (per the manual) |
|---|---|
| Goodman — older single-LED | External lockout after 3 failed ignition attempts; auto-resets after 1 hour. Also reset by removing the thermostat signal or cutting power for 5+ seconds. |
| Goodman — GMEC96 | Separate lockout codes for retries (7 flashes), recycles (8), and a limit circuit open over 5 minutes (11). The chart treats each as its own diagnosis. |
| Carrier / Bryant | Code 13 (limit/rollout lockout) and code 14 (ignition lockout) auto-reset after 3 hours. Code 21, gas heating lockout, never auto-resets. |
| Trane | 2 flashes = system lockout, retries or recycles exceeded. The board stores the last 4 faults — read them before resetting, they are the story of why. |
| Lennox | Watchguard is Lennox’s lockout mode: burners failed to ignite, a limit stayed open over 3 minutes, or flame was lost 5 times in one cycle. See the Watchguard page. |
| Rheem / Ruud | Display code 10 = 1-hour lockout, shown alternating with the fault that caused it — four failed ignitions, or five flame losses. |
| York | 7 red flashes: lockout after 3 ignition tries, 1-hour lockout, then it retries on its own. |
Why yours keeps doing it
Lockouts have short suspect lists, and the code that precedes the lockout names which list you are on:
- Ignition lockouts (it never lights): gas supply, a dead igniter, a coated flame sensor. Start with the code, then the basics — thermostat, filter, the gas valve at the furnace.
- Recycle lockouts (it lights, then loses flame): flame signal again, or pressure switches dropping out mid-cycle — venting and condensate move to the top of the list.
- Limit lockouts (it runs hot, then quits): airflow. Filter, registers, returns — the dullest causes and the most common ones.
The reset rule
One reset, after the basics, is diagnosis. A furnace that locks out again is not being stubborn; it is reporting. Daily lockouts mean a part is failing on a schedule, and every brand’s manual says the same thing in its own words: find the cause. The codes before the lockout — Goodman 7 blinks (and 8, in the Goodman tables), Carrier code 14, Rheem code 11 — are the ones to hand your technician.
The two rules that outrank everything on this page.
1. Smell gas? Stop reading. Leave the house and call your gas utility or 911 from outside. No code is worth diagnosing through a gas smell.
2. Never bypass a safety switch — no jumping a pressure switch, no taping a limit, no propping a rollout. Those switches are the only thing between a furnace fault and a fire or carbon-monoxide problem. This library explains codes; it does not teach repairs inside the cabinet.
Go deeper by brand: Goodman · Carrier · Trane · Lennox · Rheem · York · or run your code through the decoder.
One honesty note before the tables: codes change between control boards, sometimes inside the same brand and the same decade. Every table below names the board and the manual it was transcribed from. The chart glued inside your own blower door is the final word for your furnace — if it disagrees with this page, believe the door.