York did one thing better than most: it put the diagnostic table in the user manual, not just the service literature — quarter-second flashes, two-second pause, and causes written for the person standing in the basement. The table below follows those manuals (PC9, GF9S, G8C families).
One code needs care: 6 red flashes. In the GF9S/G8C manuals it is a pressure-switch cycle lockout. In York’s modulating PC9 manual, code 6 is a modulating gas valve current failure. Same brand, two product families — the table flags it on the row itself rather than picking a winner.
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.
Which chart is yours?
User-manual table first: it covers the PC9, GF9S and G8C families and most single/two-stage York furnaces you will meet in a basement. The second, shorter table holds codes 9-11 from the fault chart of the ICM2808 control — the board that replaces York’s S1-331-03010-000 / S1-331-02956-000 boards in a large share of installed York furnaces. Coleman and Luxaire furnaces from the same Johnson Controls family often carry this control too; their door charts decide.
Red-flash codes — York user-manual table
York furnaces covered by the PC9 / GF9S / G8C user and service manuals (Unitary Products Group). Flashes are 1/4 second on, 1/4 second off, with a 2-second pause between groups.
| What you see | What the manual says it means |
|---|---|
| Slow green flash | Normal operation — No call for heat, everything fine. |
| Slow amber flash | Normal operation with a call for heat — The furnace is being asked for heat and is answering normally. |
| Rapid red flash | Twinning error — incorrect 24V phasing — Twinned furnaces wired out of phase with each other. |
| LED on (continuous) | Internal control failure — Per the manual: if the failure is internal to the control, the light stays on continuously. |
| 1 red flash | Flame sensed when there was no call for heat — The control turns on the inducer and the blower when this happens. The manual’s typical cause: a gas valve that leaks through or is slow to close. |
| 2 red flashes | Pressure switch stuck closed — The control confirms these contacts are open at the start of every cycle. Faulty switch or miswiring, per the manual. |
| 3 red flashes | Pressure switch stuck open — The manual lists the full suspect line-up: faulty combustion air blower, blocked vent pipe, blocked air intake pipe, blocked condensate drain, faulty pressure switch hose, or a faulty pressure switch. Full page → |
| 4 red flashes | High limit switch open — or the 24V fuse is open — Manual causes: dirty air filter, improperly sized duct system, faulty blower motor, restricted circulating airflow. The filter is on that list for a reason. |
| 5 red flashes | Rollout switch or auxiliary limit switch open — The rollout switch is a manual-reset switch on the burner box. The manual says reset it only after correcting what opened it — and if it trips again, that is a service call, full stop. |
| 6 red flashes | Pressure switch opened 4 times during the call for heat — From the GF9S/G8C manuals: cycle lockout — the unit locks out for one hour, then restarts. Note for modulating PC9 furnaces: York’s PC9 manual gives code 6 as a modulating gas valve current failure instead. Two York families, two meanings — check which furnace you own. |
| 7 red flashes | Lockout due to no ignition — Three tries for ignition, then a one-hour lockout, then it tries again. If yours keeps reaching 7, it is asking for a technician, not another reset. |
| 8 red flashes | Lockout due to too many flame recycles — Flame lost five times in a single heating cycle. The ignition works; keeping the flame is the problem. |
Source: York PC9 / GF9S User Manuals (Unitary Products Group), Furnace Control Diagnostics. Read the document (fetched 2026-10-30).
Higher codes — later York control boards
From the fault-code chart of the ICM2808 control built to replace York boards S1-331-03010-000 and S1-331-02956-000 — the chart that ships with the board used across a large share of York furnaces.
| What you see | What the manual says it means |
|---|---|
| 9 red flashes | Grounding or line polarity fault — The supply wiring or ground is wrong for this board. |
| 10 red flashes | Gas flow with no call for heat — Gas moving when the board never asked. Furnace off, call in. |
| 11 red flashes | Limit switch open / blower failure — An extended limit-open condition, with blower failure on the suspect list. |
Source: ICM2808 Furnace Control Installation Guide - fault code chart for York boards S1-331-03010-000 / S1-331-02956-000. Read the document (fetched 2026-10-30).
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.
Questions
Can I reset a York rollout switch myself?
York’s manual describes the rollout switch as manual-reset with a button in its center — and in the same breath says to correct the failure condition first, and that if it trips again it is a service call. Our line is stricter: a rollout that opened once gets a technician, because what it protects against is flame escaping the burner box.
Why does my York show a green or amber light?
Those are status colors, not faults: slow green is normal operation, slow amber is normal operation with a call for heat. Faults are red.
Where these meanings come from
Transcribed 2026-10-30 from the manufacturers’ own documents — not from other blogs:
- York PC9 / GF9S User Manuals (Unitary Products Group), Furnace Control Diagnostics — read it
- ICM2808 Furnace Control Installation Guide - fault code chart for York boards S1-331-03010-000 / S1-331-02956-000 — read it