Home › Furnace Blinking Light Codes: Every Flash Pattern by Brand

Furnace Blinking Light Codes: Every Flash Pattern by Brand

All brands Furnace display showing BLINK CODES — FixCode Guide error code graphic

Most furnaces have no screen. What they have is one small LED on the control board, visible through a window in the door, and that single light carries every message the board can send — normal standby, a call for heat, and each fault, all encoded as blinks. This page is about reading that light properly: how to count without fooling yourself, how the counting systems differ between brands, what the colours mean, and the order to check things when the light blinks but no heat comes.

Safety first. Read the light through the door's sight glass, not by opening the cabinet: a door switch cuts power on many furnaces, and a board that loses power forgets the pattern you came to read. Never hold a door switch closed with tape or jumper a pressure, limit or rollout switch to watch a cycle run. Gas smells, scorch marks or a sounding CO alarm end the investigation: controls off, people out if the alarm continues, technician and gas utility called.

Why a furnace talks in blinks at all

A blinking LED survives conditions that kill screens. It works in a freezing garage, costs almost nothing, has no language to localise, and can be read through a peephole in the door without exposing the owner to the cabinet's wiring. So furnace makers kept the LED long after displays became cheap, and built a small language on it: short blinks counted like digits, long blinks, pauses of different lengths, steady states, and on newer boards, colour. The limitation is bandwidth — one light can only say one thing at a time, slowly — which is why reading it well is a skill of patience rather than knowledge.

Everything on this page follows from that constraint. Because the message repeats in a loop, you never need to catch it first time. Because the loop is slow, a thirty-second phone video captures several full repetitions and settles every counting argument. And because the same light also reports ordinary states — standby, a heating call, a blower finishing a cycle — the first question is never 'what fault is this' but 'is this a fault at all.' Brands answer that question differently, which is what the next sections separate out. One light, patiently read, can carry a whole service call's worth of information.

Counting correctly: two full repeats, and find the long pause

Stand in front of the sight glass and resist counting the first cycle you see; you arrived mid-sentence. Watch until the pattern has repeated completely twice. Every blink code has a boundary, and the boundary is the long pause — the clearly longer dark gap after which the same sequence starts again. Flashes inside the sequence are evenly spaced; the pause is not, and learning to spot it is the whole technique. Count only the flashes between two long pauses, and write the count down before you touch anything.

Two refinements save most misreads. On two-digit systems, a shorter pause splits the pair: the first group of flashes is one digit, the second group is the other, and only then comes the long pause. And record before you reset — a phone video taken now is worth more than a confident memory later, because cycling power to 'see if it clears' also clears the board's stored pattern on many models. If the furnace is mid-cycle, wait for it to finish or fail; a pattern read while the blower is still running off a completed call may be a status, not the fault that interrupted the previous cycle. A written count with the date beside it also survives the walk to the door chart, which a memory of 'about five flashes' does not.

Single counts, digit pairs and pattern boards

The largest family is the single count: the LED flashes a number of times, pauses, and repeats the identical count. Goodman, Trane and York boards of many generations all speak this way, and the door chart translates each count. York's counted codes on its colour boards belong to this family too, with colour layered on top of the count. The second family builds a two-digit number from two groups — Carrier's version flashes the first digit as short blinks and the second as long blinks, a distinction owners miss when they count twenty-two flashes and go looking for a code that does not exist. If your total seems implausibly large, suspect a pair and recount by groups.

Lennox deserves a separate word because it straddles the families. Plenty of Lennox boards count flashes like the first group, but the brand also uses a calm, slow heartbeat blink to say 'powered and waiting,' and its current models abandon blinking for faults altogether in favour of letter-number codes on a small display. So on a Lennox, a gentle regular blink with a warm house is the board's idle breathing, not a one-flash fault — check the door chart's description of normal before treating any slow pattern as an error.

Colour is a second channel: York's three colours, Trane's red, and the steady states

York's later control generation gives the LED three colours and assigns each a territory. Green covers the ordinary: a slow green flash is normal operation with no call for heat, and green also reports housekeeping such as an empty or freshly cleared fault memory. Amber accompanies work: a slow amber flash means normal operation with a call for heat in progress, other amber counts mark reduced-capacity running when airflow or venting is restricted, and a rapid amber flash warns that flame sensing is weak. Red is where faults live — counted red flashes name the failure, and a rapid red flash flags a wiring/phasing problem on twinned systems.

Elsewhere, colour is fixed and state carries the meaning. Trane's board LED is red, and its vocabulary is count plus the three steady states every brand shares in some form: steadily on, steadily off, and flashing too fast to count. Those states mislead more owners than any count — a steady light means 'internal control fault' on some boards and 'perfectly normal' on others, sometimes within the same brand's generations, as Goodman's charts show. The door chart's first three entries usually define your board's steady states; read them before any numbered code, and photograph them for the next time the light puzzles you.

Slow blink, fast blink — and why the answer depends on the brand

Owners reasonably ask whether a slow blink or a fast blink is 'the bad one.' There is a pattern underneath the variation: on several widely used boards a slow, lazy flash means the control is powered and idle — no call for heat has arrived — while a faster regular flash means a call is active and the furnace is working or trying to work. York builds exactly this distinction into its colours, slow green for idle and slow amber for a heat call, and many Trane boards similarly change their flash rate between standby and a call.

But treat that as a tendency, not a law. A rapid flash is a defined fault on some charts, a factory test state on others, and 'flame signal weak' on York's amber. The rate alone never diagnoses anything; rate plus colour plus count, matched against your own door chart, does. What you can safely conclude from rate is behavioural: a board whose pattern changes when you raise the thermostat has heard the call, while a board that blinks its idle pattern no matter what the thermostat says is telling you the call never arrived — a thermostat, wiring or power problem rather than a furnace fault.

Blinking but no heat: the triage order that wastes no steps

When the light blinks and the house stays cold, resist starting with the code. Start with the call: thermostat set to heat, setpoint above room temperature, batteries and schedule checked — a board blinking its idle pattern is waiting for instructions it never received. Next, power: breaker on, furnace switch on, and the blower door fully seated so its switch is made. Then airflow, the cheapest fault in heating: a filter clogged enough to trip limits, registers and returns closed off, a blower that never starts. Then the condensate path on high-efficiency models, where a backed-up drain or overflow switch can stop a cycle the board barely reports.

Only after those four gates is the blink count the main evidence — and by then it is far better evidence, because you know the furnace was called, powered, able to breathe and able to drain when it produced the pattern. Count it twice, video it, and match it on your brand's list below. If the count names ignition, pressure or flame, the remaining work is technician territory; if it names a limit, your filter and register findings decide whether it was a one-off or a warning. A pattern that returns after one honest reset is a fault confirmed, not a nuisance to keep clearing.

Carrier furnace error codes

Read a Carrier light as two numbers, not one long count: brief flashes give the first digit, longer flashes give the second, then a long pause ends the pair. Count the pair twice — the most common Carrier misread is adding both groups into a single impossible total. The board stores recent codes, so the pattern may describe the last fault rather than the present one; if the furnace is currently heating normally, treat the pair as history worth noting, not a live emergency.

Code	Meaning
12	Blower on after power-up — not a fault: the control runs the blower for ~90 seconds at start-up when a thermostat call was present during a power interruption (a status/safety behaviour).
13	Limit circuit lockout — the control locked the furnace out because a limit or flame rollout switch in the limit circuit stayed open longer than 3 minutes, or limit trips came in succession (10 successive trips during high-heat; the variable-speed generation also locks out after 3 successive trips during low-heat). The control auto-resets after 3 hours.
14	Ignition lockout — the furnace tried to light three times and failed, so the control locked out (typically retrying after ~1 hour).
21	Gas heating lockout — Carrier's service label words it: 'STATUS CODE 21 — GAS HEATING LOCKOUT. Control will NOT auto reset. Check for: mis-wired gas valve; defective control (valve relay).' The control has shut down gas heating and, uniquely among Carrier's common lockouts, it will not clear itself with time.
11	No previous code — the control's stored fault history is empty; this is not a fault
15	Blower motor lockout — the blower failed to reach 250 RPM or to communicate within 30 seconds of turn-on, in two successive heating cycles
22	Abnormal flame-proving signal — flame is proved while the gas valve is de-energised; the inducer runs until the fault clears
23	Pressure switch did not open — a pressure switch is still closed (made) when a call for heat begins

Full list: Carrier Furnace Error Codes List — every verified Carrier code with causes and first fixes.

Goodman furnace error codes

A Goodman light is a single-count light on most boards: flashes, a pause, the same count again. The reading skill that matters here is the steady states — depending on the board generation, a continuously lit LED is either normal standby or a failed control, and a dark LED always means power is not reaching the board. Goodman's own charts define which, and generations differ, so identify your board's normal from the door before interpreting anything else.

Code	Meaning
5 Flashes	On Goodman's single-stage boards: flame sensed without the gas valve energised — the GMES80 wiring diagram prints it verbatim: '5 FLASHES = FLAME SENSE WITHOUT GAS VALVE [ENERGISED]'. On Goodman's two-stage boards the same count means something else entirely: open rollout switch or open control board fuse. The generation split is documented in the what — read it before acting on any of it.
9H	Not a standard published Goodman furnace fault — treat as a platform/display-specific reading to be decoded with the model number (Goodman's systems are LED blink codes and E-codes on communicating models).
F02	Not a standard Goodman consumer fault rendering — Goodman furnaces report faults with board LED blink patterns and, on communicating models, E-codes (E02 etc.). 'F02' is most likely a mis-read blink count or a communicating-thermostat rendering; decode via the model's chart.
H6	Not a standard published Goodman furnace fault code — decode via the model's LED blink pattern / communicating-system chart and the observed symptom.
1 FLASH	System lockout after excessive ignition retries; two-stage boards: flame sensed with no flame present
2 FLASH	Pressure switch stuck closed before the inducer starts
3 DOUBLE FLASHES	Second-stage pressure switch stuck open during high-stage inducer operation
3 FLASH	Pressure switch failed to close (stuck open) when the inducer ran

Full list: Goodman Furnace Error Codes List — every verified Goodman code with causes and first fixes.

Lennox furnace error codes

On many Lennox boards the light's slow, regular blink is the sign of a healthy idle furnace — the pattern owners most often misreport as a fault. Fault patterns break that rhythm with distinct counts defined on the door chart. If your Lennox has a small character display instead of a plain LED, you are on the newer system: it prints letter-number codes, and blink-counting advice does not apply to it at all. Read what is printed, letter included.

Code	Meaning
E201	Communication fault on Lennox communicating (iComfort) furnaces — the system components have lost communication (E201 is the iComfort comms-loss alert).
E105	Device communication problem; no other devices found on the RSBus communication system
E110	Low AC line voltage detected by the control
E125	Control hardware failure, including A/D electronics and flame test circuitry (five-minute lockout)
E131	Corrupted control parameters; non-volatile data corruption (communicating mode)
E150	A2L refrigerant leak detected; thermostat lockout while mitigation runs
E154	Refrigerant leak detector sensor 1 communication lost

Full list: Lennox Furnace Error Codes List — every verified Lennox code with causes and first fixes.

Trane furnace error codes

Trane's light is red and single-count: flashes grouped between clear pauses, matched to the chart inside the door. Two cautions from Trane's own generational changes — some counts changed meaning between board revisions, so a chart from a video may describe a different furnace than yours; and on many Trane boards the flash rate itself shifts between no-call and call-for-heat states, so note the rate as well as the count when you record the pattern for a technician.

Code	Meaning
3 Flashes	Pressure switch fault — the pressure switch did not close (or the inducer/vent proof failed) on Trane furnaces with LED blink diagnostics.
5 Flashes	Flame sensed when no flame should be present — Trane's chart wording (UC-series installer's manual and the verified chart): '5 Flashes: Flame sensed when no flame should be present.' The flame sensor is reporting a flame at a time when the gas valve is not energised and no flame may exist.
7 Flashes	Gas valve circuit error — Trane's chart wording is exactly that: '7 Flashes: Gas valve circuit error.' The integrated control has detected a fault in the electrical circuit between itself and the gas valve: the wiring, the valve's coil, or the control's own valve output.
E09	Platform-specific Trane code (communicating/ComfortLink-era systems render faults in E-format) — not part of Trane's classic blink-code list; the model/thermostat documentation defines the branch.
2 Flashes	System lockout; ignition retries or recycles exceeded
4 Flashes	Open temperature limit circuit; the furnace overheated and shut the burners down
6 Flashes	115 volt AC power reversed, ignitor (triac) fault, poor grounding, or system voltage too low
8 Flashes	Low flame sense signal

Full list: Trane Furnace Error Codes List — every verified Trane code with causes and first fixes.

Rheem furnace error codes

If you are standing in front of a Rheem looking for blinks to count, stop: Rheem's furnace control reports on a seven-segment display, not by flash patterns. The display shows a standby zero at rest, a letter while a mode runs, and a fault as two digits shown one after the other in a repeating cycle. Your reading task is simply to watch one full cycle and write down both digits in order. Any 'Rheem flash code' list that assigns meanings to blink counts is describing some other furnace.

Code	Meaning
11	Failed ignition — the furnace control ran an ignition attempt and flame was not established and proved; the code is displayed after the first failed attempt and stays until ignition succeeds or the failures escalate to lockout.
61	Blower fault — blower unable to run. Critical: no operation in any mode. Rheem also declares 61 when the main limit has been open over 150 seconds during a heat call (the display then alternates 61 and 22): the control reads a limit that cannot re-close as a dead blower, because the blower should be carrying the heat away. A fourth dead-blower declaration in one heat call enters hard lockout.
0	Standby — not a fault: the display reads 0 when no fault is present and there is no thermostat call; the furnace is idle
10	One-hour lockout (soft lockout) — gas heating is shut down for one hour; the display alternates 10 with the causing code (11, 13, 14, 59, 61 or 93)
12	Low flame sense — the flame sense current from the flame rod is weak or marginal; Rheem classes this non-critical and heating continues normally
13	Flame lost — after a successful ignition the flame was properly sensed and then was no longer sensed, while a valid heat call is still present
14	Unexpected flame — flame is sensed while the gas valve is supposed to be off. Rheem calls this extremely critical; the furnace will not operate
20	Twinning fault — on a twinned pair (two furnaces, common duct system and thermostat, linked by the TWIN terminal), twinning was detected and then lost in the same power cycle

Full list: Rheem Furnace Error Codes List — every verified Rheem code with causes and first fixes.

York furnace error codes

Read a York light in two passes: colour first, count second. Green patterns are the board reporting normal states or memory housekeeping; amber patterns accompany calls for heat or cooling, reduced-capacity running, or a weak flame signal when the amber flashing turns rapid; red patterns are faults, counted like other brands' codes, with a rapid red reserved for a twinning/phasing problem. The flashes themselves are quick, evenly spaced beats separated by a longer off-period that marks where the count restarts.

Code	Meaning
2 red flashes	Pressure switch stuck closed — the pressure switch contacts are closed when they should be open. BOTH tri-colour generations agree on this code. Standard boards confirm it at the start of each heat cycle, before the inducer runs; modulating boards phrase the same report precisely: pressure switch closed with inducer pressure below the pressure switch setpoint (the switch is closed when it should be open).
3 red flashes	Pressure switch stuck open — the pressure switch contacts are open when they should be closed: the normally open contact did not close after the inducer was energised, so draft was never proven and the furnace will not light. The modulating generation phrases the same report more precisely: pressure switch open with inducer pressure above the pressure switch setpoint (the switch is open when it should be closed).
4 red flashes	Limit switch open — a limit switch has opened its normally closed contacts because the furnace overheated, and the control runs the supply air blower and inducer while the condition exists. GENERATION NOTE: on modulating boards York's definition is wider — high limit switch open OR defective temperature sensor OR 24-volt fuse open. On standard boards the detailed manual text defines 4 red flashes as the main limit switch only (GF9S wording: a primary or auxiliary limit switch).
7 red flashes	Ignition lockout — lockout due to no ignition: flame could not be established in three ignition tries. BOTH tri-colour generations agree on this code. The control locks out for one hour, then tries again. The standard manuals detail it as a no-light condition that occurred 3 times (2 retries) during the call for heat before locking out.
1 amber flash	Modulating boards only: normal operation with a call for cooling
1 red flash	Both tri-colour generations: flame was sensed/present when there was no call for heat and no power supplied to the gas valve; the control runs the inducer and supply air blower
2 amber flashes	Modulating boards only: normal operation with a call for heat — the modulating equivalent of the standard boards' slow amber flash
2 green flashes	Both generations, seen only during stored-code retrieval: no error codes in memory — the LAST ERROR playback found an empty history

Full list: York Furnace Error Codes List — every verified York code with causes and first fixes.

Blinking states that are completely normal

A healthy furnace blinks a surprising amount. Standby heartbeat patterns tell you the board has power and is waiting. Call patterns announce that the thermostat has asked for heat and the sequence is under way. End-of-cycle patterns cover the blower running on after the burners stop, and power-restore states explain the blower starting by itself after an outage. York formalises several of these in green and amber; other brands print them at the top of the door chart, above the faults, precisely because the makers know owners read them as faults.

The test that separates normal from fault is never the blink alone — it is the blink plus behaviour. House warming, cycle completing, thermostat satisfied, light settling back to its idle rhythm: that is a status. House cooling, cycle aborting at the same point each time, pattern identical across repeated attempts: that is a fault with a blink for a name. When in doubt, raise the thermostat and watch one full cycle from call to blower-off; a normal board will walk through its states in order and come to rest. Manufacturers know owners misread these patterns, which is why the normal ones are printed on the same door chart as the faults instead of being left in a separate manual nobody opens.

When the light is dark

No light at all is also a message, and the simplest one the board can send: it has no power, or it has failed. Work from the wall inward. Breaker first, then the furnace's own service switch — a switch near the unit that gets knocked off by stored boxes more often than any component fails — then the blower door, whose safety switch cuts power when the door is ajar. Inside that chain sits a small automotive-style fuse on the control board that sacrifices itself to low-voltage shorts; a dark board with good household power often ends there. Also check for a plug, receptacle switch or inline switch a previous installer added near the unit — dark-board hunts have ended at a switched-off outlet more than once.

Only when power is proven at the board and the light stays dark does the board itself become the suspect, along with the transformer that feeds it low voltage. Both are technician diagnoses, partly because confirming them means metering live circuits inside the cabinet. Report a dark board accurately — 'no light, breaker and switch on, door seated, house lights normal' — and you have already done the useful half of the diagnosis from outside the machine, before anyone opens a panel.

When the blinking is the symptom, not the code

There is one situation this page deliberately hands off: the display or panel itself behaving strangely — a thermostat screen blinking, a board light flickering irregularly rather than patterning, lights that dim when the blower starts. Irregular flicker is not a code in any brand's language; it points at power quality, loose low-voltage connections or a failing control rather than a named fault. Our companion guide to a blinking furnace display works through those causes in order, and it is the right next read when your light will not settle into a countable, repeating pattern. Keep that distinction in mind before you start counting anything at all.

Flicker has its own short list of usual causes: a thermostat wire nicked or loose at a terminal, household voltage sagging as a large load starts, a transformer weakening under load, or a control board beginning to fail. None of these can be confirmed from the doorway, and none of them should be chased by wiggling wires inside a live cabinet. What you can usefully record is when the flicker happens — at blower start, during ignition, randomly through the day — because that timing is the clue a technician will build the diagnosis on, and it costs you nothing but attention to capture it accurately.

How to diagnose any furnace code

Work the problem in this order — and stop at any point where gas, combustion or mains wiring is involved, because those belong to a licensed HVAC technician: (1) record the code exactly: count LED flashes slowly, twice, or photograph the alphanumeric display; (2) check the free things homeowners legitimately own: the thermostat is calling for heat, the furnace power switch and breaker are on, the filter is not clogged solid (a starved furnace overheats and locks out on limit codes), all vents and the return are open, and the condensate drain is not blocked on condensing models; (3) reset once — at the power switch, off for 30 seconds — then watch a full call for heat from the beginning: inducer, ignition, flame, blower, in that order; where the sequence stops is the fault family the code names; (4) a code that returns immediately is an active fault — do not keep resetting a lockout, especially any flame or limit code; (5) everything inside the burner compartment — flame sensor cleaning is the one grey area many manuals allow owners, but gas valves, burners, heat exchangers and control boards are professional work. If you smell gas at any point, leave and call the gas utility, not a helpline.

Frequently asked questions

What do furnace blinking light codes mean?

They are the control board's fault and status reports, encoded as counted flashes of a single LED because most furnaces have no screen. Each brand's door chart translates the counts: one count may report a pressure-switch proof failure, another an ignition failure, another a limit opening. Some patterns are not faults at all but normal states such as standby or an active call for heat. Count the flashes between long pauses, then match the count — and the colour, on York — to your brand's list.

My furnace red light is blinking — is that always a fault?

Usually, but not always. On Trane boards the LED is red by design, so red is simply the colour of every message including normal ones on some generations. On York's three-colour boards, counted red flashes do name faults, while green and amber carry the normal states. The colour only means something inside your brand's system: check whether your board uses red for everything or reserves it, which the first lines of the door chart will tell you.

Where is the furnace flashing light codes chart for my exact model?

Glued inside the blower compartment door of your own furnace. Manufacturers print the chart for the exact control board fitted at the factory, including its normal patterns and steady states, which no generic chart reproduces reliably. Photograph it once and keep the photo with your code log. The brand lists linked from this page cover the verified codes for each maker's main systems, but where a web list and your door chart disagree, your chart wins.

How do I read a furnace blinking light without miscounting?

Watch two full repetitions before counting, find the long pause that separates repetitions, and count only the flashes between two long pauses. On two-digit systems, split the count at the shorter mid-pause into its two groups. Film thirty seconds with your phone before resetting anything — power cycles erase stored patterns on many boards — and never open the door to look, because a door switch can cut power and clear the very pattern you are reading.

Why is my furnace light blinking but there is no heat?

Either the pattern is a normal standby or call state and the failure sits elsewhere, or the pattern is a fault that stopped the sequence. Check in order: the thermostat is actually calling for heat, the breaker and furnace switch are on, the door is fully seated, the filter is not clogged, and a high-efficiency unit's condensate drain is not backed up. Then count the pattern and match it to your brand's list — a board blinking its idle rhythm throughout points back at the call or power, not the burners.

Are furnace LED codes the same as the codes on my thermostat?

On communicating systems they are two views of the same fault reporting: the wall control shows the fault as a number or letter-number code and keeps a history, while the board may still blink its own version. On conventional systems the thermostat shows nothing and the LED is the only reporter. The two will not always match digit for digit, because the thermostat displays the system's numbering while the LED speaks the board's — give a technician both, exactly as each device showed them.

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