An open limit circuit means the furnace's overheat protection opened the safety chain: the main limit, an auxiliary limit, or the rollout switch. The gas valve shuts the moment any of them opens. Goodman's chart tells the technician to check temperature rise, duct static, gas pressure, burner alignment, and the wiring to every limit — a list that starts, in practice, with why the furnace is running hot.
Furnaces run hot when air cannot move. That is why the checklist leads this page: do the filter and the registers first, honestly, before you conclude anything is broken. If the furnace then runs and stays running, you have your answer and it cost you a filter.
Homeowner checks — the safe list:
- Air filter first. On limit codes the filter is the cause often enough that a technician will ask about it before anything else.
- Walk the house and open every supply register. Closed or blocked registers strangle airflow.
- Check the returns: rugs, furniture, and storage boxes parked against return grilles count.
- If the code comes back on a clean filter with everything open, the blower or the limit switch itself needs a technician.
4 red flashes: Open limit circuit — main limit, auxiliary limit, or rollout switch
Homeowner checks
The furnace got too hot somewhere, or the safety chain opened. The manual tells the tech to check temperature rise, duct static, and the wiring to every limit. For you, airflow is the lever.
From the table: Red-LED chart — two-stage 96% furnaces — source: Goodman GCEC960803BN Installation Instructions, Troubleshooting Chart, pp. 55-56 (read the document, fetched 2026-10-30). Covers: GMEC96 / GCEC96 and their Amana twins — the current two-stage condensing furnaces with a green/amber/red LED trio on the board.
Both charts agree here
The older single-LED chart also gives 4 flashes as an open limit, and its manual spells out the airflow story: "a primary limit will open due to excessive supply air temperatures — a dirty filter, excessive duct static, insufficient air flow." One caution from the same page: if the open switch turns out to be the rollout, that is not an airflow errand. Rollout means flame misbehaved at the burners; the switch is manual-reset, and it gets a 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.
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.