Updated 2026-06-25
Rheem Furnace Error Codes & What They Mean
Compiled & reviewed by Nikolai Tsyrenov · Updated 2026-06-25
How do I read Rheem furnace error codes?
Rheem furnaces signal faults by flashing a diagnostic LED a set number of times, where the flash count is the fault code.
How to read Rheem furnace codes
Rheem furnaces signal faults by flashing a diagnostic LED a set number of times, where the flash count is the fault code. Find the LED through the clear viewport on the blower-compartment door and count the flashes between the longer pauses, then match the count to your unit's data-plate or installation-manual chart. Codes differ between standard single-stage boards and modulating/two-stage/communicating models, and newer multi-LED boards use separate POWER/STATUS/FLAME indicators.
Rheem furnace code list
| Code | What it means (tap for fixes) |
|---|---|
| 1 flash | Soft lockout (about 1 hour) — no flame was sensed after four ignition trials; the control locks out and will auto-retry. |
| 2 flashes | Pressure switch open — the negative pressure-switch circuit is open (the switch did not close while the inducer runs). |
| 3 flashes | Limit switch open — the high-limit (or rollout) safety control has opened, typically from overheating or low airflow. |
| 4 flashes | Pressure switch closed — the switch is stuck closed (its contacts are closed when they should be open, e.g. before the inducer starts). |
| 5 flashes | Twinning circuit fault — a fault in the twinning connection used when two identical furnaces share one thermostat/ductwork (only applies to boards with the twinning feature). |
| Slow green flash | Normal operation — the control board has power and no active fault. If the furnace isn't heating, check the thermostat and that the door panel is fully seated (the door switch must be engaged). |
| STATUS LED steady on | On multi-LED boards (separate POWER/STATUS/FLAME LEDs), a steady STATUS LED indicates normal operation with no stored fault. |
| STATUS LED 6 flashes | On multi-LED boards, six STATUS flashes indicate AC line and neutral are reversed (incorrect polarity). This is an electrical fault for a technician or electrician — do not rewire furnace power yourself. |
| FLAME LED rapid blink | On boards with a dedicated FLAME LED, a rapid blink indicates the control senses flame when none should be present (possible gas valve not fully closing). Set the thermostat OFF and call a technician promptly. |
| FLAME LED slow blink | On boards with a dedicated FLAME LED, a slow blink indicates a weak/marginal flame-sense signal (often a dirty flame sensor). Have it serviced before it becomes a no-heat lockout. |
⚠️ Safety first. Gas furnaces burn fuel and produce combustion gases. If you ever smell gas (a rotten-egg or sulfur odor), hear hissing, or your carbon-monoxide alarm sounds, do not touch light switches, thermostats, or the furnace — leave the home immediately and call your gas utility's emergency line or 911 from outside. Homeowners should limit themselves to simple, safe steps: setting the thermostat, checking and replacing the air filter, confirming the furnace switch and breaker are on, keeping supply registers and return grilles open, and clearing snow, ice, or debris from outdoor vent and intake terminations. Never bypass, jumper, or reset safety switches (limit, flame-rollout, or pressure switches), never open the gas valve or burner compartment, and never attempt combustion, electrical, or control-board repairs yourself. Error codes point toward a problem but are not a substitute for proper diagnosis — when in doubt, turn the system off and call a licensed HVAC technician. Keep working carbon-monoxide detectors on every level of your home.
Rheem furnace code FAQ
How do I read the error code on a Rheem furnace?
Rheem furnaces signal faults by flashing a diagnostic LED a set number of times, where the flash count is the fault code.
Where is the diagnostic light on a Rheem furnace?
It's on the control board, usually visible through a small sight glass on the lower blower-compartment door. You may need to remove the door panel to read it clearly.
What is the most common Rheem furnace code?
1 flash — Soft lockout (about 1 hour) — no flame was sensed after four ignition trials; the control locks out and will auto-retry.
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Sources: my.rheem.com. General information for homeowners — confirm against your furnace's installation manual.