If your Rheem furnace has a blinking status light on the control board behind the blower door and no steady heat, that light is a flash code telling you why it stopped. Rheem and its sister brand Ruud share the same control boards, so the same chart applies to both. The catch: Rheem's own literature only documents a handful of these codes clearly, and a lot of the higher-count charts online come from third parties that don't agree with each other. This guide separates what Rheem actually publishes from what's lower-confidence, so you don't buy a part off a bad chart.
Reading the code: count the blinks between pauses on the board's status LED — a steady group of flashes, a pause, then it repeats. Flash-code meanings can vary by control-board generation, so always confirm the count against the diagnostic label inside your unit — printed on the board cover or the blower-compartment door — before you buy a part.
Rheem furnace flash codes
| Flashes | Meaning | Typical cause |
|---|---|---|
| 1 | Soft lockout — ignition failed after 3 tries | Dirty flame sensor, a bad hot-surface igniter, or low gas |
| 2 | Pressure switch stuck open | Blocked vent or flue, a weak inducer, or a condensate backup |
| 3 | Limit switch open | Dirty filter, blocked return or flue, restricted airflow/ducts |
| 4 | Pressure switch stuck closed | Stuck switch or contacts, or an inducer/wiring fault |
| 5 | Twinning circuit failure | Twinning-kit wiring fault on paired furnaces |
| 6 ⚠ | Third-party: reversed line/neutral polarity | Miswired line and neutral or a bad ground — but see the conflict note below |
| 7 | Third-party: weak flame signal / gas valve | Dirty flame sensor, a marginal flame, or a gas-valve issue |
| 8 | Third-party: igniter failure | A cracked or open hot-surface igniter |
| 9 ⚠ | Third-party: flame rollout | Rollout from a blocked heat exchanger or poor combustion — but see the conflict note below |
About codes 6 through 9
This is where you have to be careful. Rheem officially documents roughly codes 1 through 5. Codes 6 through 9 come from third-party and aggregator charts, and they are lower-confidence — treat them as a starting point, not gospel.
They also conflict on 6 versus 9. Some charts list 6 = reversed line/neutral polarity and 9 = flame rollout; others swap them, listing 6 = flame rollout and 9 = polarity. We don't guess between them. Both readings point at real, serious faults — a rollout is a combustion/heat-exchanger safety issue and a polarity fault is a wiring problem — so on a 6 or a 9 we verify the meaning on your specific board and against the diagnostic label inside your unit before touching anything. Where two sources conflict, the label on your furnace is the authority.
Rheem EcoNet AC & heat pump codes (brief)
If it's a Rheem or Ruud EcoNet air conditioner or heat pump rather than the furnace, the outdoor control shows a 7-segment code instead of a blink count. A few common ones:
| Code | Meaning |
|---|---|
| 02 / L29 | High-pressure fault |
| 21 / L21 | Low-pressure fault |
| L4 | Locked rotor |
| 80 | Low airflow |
High- and low-pressure faults, locked rotor, and anything on the refrigerant side belong with a licensed technician — see below.
Common causes
Across the furnace codes above, most common first:
- Dirty flame sensor — the usual reason behind a 1-flash ignition lockout (and a third-party 7).
- Dirty filter or restricted ducts — behind a 3-flash limit trip.
- Blocked vent, clogged condensate, or a weak inducer — behind a 2- or 4-flash pressure-switch fault.
- Failed hot-surface igniter — a furnace that never lights (and a third-party 8).
- Rollout or a polarity/wiring fault — the serious end, tied to the conflicting 6/9 codes.
The usual fix
Our tech reads the stored flash code, then confirms it rather than trusting the chart alone: clean or replace the flame sensor and measure the flame signal, check and change the filter, verify the inducer and venting draw properly, test the pressure and limit switches, and inspect the igniter and gas pressure. On any code that points at rollout or a polarity/wiring fault, we check the heat exchanger, combustion path, and incoming power before returning the furnace to service. A cleaned sensor or restored airflow clears many Rheem calls; when a part has truly failed we replace it and confirm a full, clean heat cycle.
DIY vs. calling a pro
Safe to try yourself first (free):
- Turn the furnace off and change a dirty filter, wait 20–30 minutes, and restart — this clears a large share of 3-flash limit codes.
- Open blocked supply and return vents and clear anything sitting over a return.
- Power-cycle at the switch or breaker to reset a soft lockout after fixing airflow.
Call a pro when:
- A code returns after a fresh filter, or you see a 1-flash ignition lockout that won't clear.
- You get a 6 or 9 and need the meaning confirmed — do not assume polarity versus rollout from a chart.
- You smell a hot or burning odor, or the furnace won't light at all.
Gas, line-voltage electrical, and any refrigerant or compressor work — including the EcoNet high/low-pressure and locked-rotor codes above — belong with a licensed technician (EPA 608 certified for refrigerant handling). A furnace that keeps overheating or rolling out can crack the heat exchanger, which is a carbon-monoxide risk.
What it costs in the Bay Area
Many Rheem codes resolve with a filter or a cleaned flame sensor. When a part is needed, in our pricing a flame sensor runs about $90–$250, a hot-surface igniter $120–$350, and a control board $200–$600, depending on the model. We charge a diagnostic fee that's credited toward the repair when you approve the work, with a firm, upfront price before any work begins.
Book Rheem furnace service
Triton services Rheem and Ruud furnaces — plus every major brand — across the SF Bay Area & Peninsula, with same-week and often same-day appointments. If your Rheem is blinking a code, we'll read it correctly, verify it on the unit, and get your heat back safely.
Call (888) 993-5699 or book online for same-day furnace service.
Related pages
- HVAC Repair in the SF Bay Area — our full heating & cooling hub
- Furnace Not Heating / No Heat — the symptom behind a limit or pressure code
- Furnace Won't Ignite / No Ignition — the symptom behind a 1-flash lockout
- Rheem / Ruud HVAC Repair — brand service hub
- Furnace Repair in Hayward — same-day service in your city
Frequently asked questions
What does a blinking light on my Rheem furnace mean? The status LED on the control board flashes a count between pauses, and that count is a fault code. Rheem and Ruud share these boards. A 1-flash is a soft ignition lockout, a 2 or 4 is a pressure-switch fault, a 3 is an open limit switch, and a 5 is a twinning-circuit fault. Count the blinks between pauses and confirm the count against the label inside your unit.
How many flash codes does Rheem actually document? Rheem clearly documents roughly codes 1 through 5. Codes 6 through 9 come from third-party and aggregator charts and are lower-confidence, so treat them as a starting point rather than a definite answer, and verify the meaning on your own board before buying a part.
Why do sources disagree on Rheem code 6 and code 9? Some charts list 6 as reversed line and neutral polarity and 9 as flame rollout, while others swap them. We do not guess between them because both point at serious faults, a combustion or heat-exchanger issue and a wiring issue. We read the code on your specific board and confirm it against the diagnostic label inside your unit.
Is a Rheem 1-flash ignition lockout serious? It means the furnace failed to light across three tries and locked out, so you have no heat. It is most often a dirty flame sensor, a weak hot-surface igniter, or a gas-supply issue. You can power-cycle it once after checking the gas is on, but a lockout that returns should be diagnosed rather than repeatedly reset.
Are Rheem and Ruud furnace codes the same? Yes. Rheem and Ruud are sister brands that share the same control boards, so the flash-code chart is the same for both. Always confirm the specific count against the diagnostic label inside your own unit, since details can vary by board generation.
How much does Rheem furnace repair cost in the Bay Area? Many codes resolve with a filter or a cleaned flame sensor. When a part is needed, a flame sensor runs about 90 to 250 dollars, a hot-surface igniter 120 to 350 dollars, and a control board 200 to 600 dollars in our pricing, depending on model. We credit the diagnostic fee toward the repair and quote a firm price first.