York Furnace Error Codes List: Every Code Explained

Every York furnace error code we could verify against York's own documentation — what it means, what usually causes it, and the first fix to try — in one table. Codes differ between model series, so treat your model's tech sheet as the final word.

How to read and retrieve error codes on York furnaces

Faults are read as a tri-colour LED on the control board, visible through the clear view port in the blower compartment door: count the flashes of one colour (the pattern repeats with a two-second pause between sets; flash timing is 1/4 second on/off on some generations, 1/3 second on others, and the slow normal-operation flash is two seconds on, two seconds off). Stored codes are retrieved with the board's LAST ERROR button — a feature York reserves for a qualified service technician: with no active thermostat call, press the button and the LED plays back up to five stored codes, most recent first; two green flashes means the memory is empty, and holding the button for more than five seconds clears it (confirmed by three green flashes). The chart printed inside your own blower door is the authority for your furnace — York's standard and modulating board generations assign different meanings to the same flash count (red 6 and red 10 among them), and online charts routinely mix the two.

The complete York furnace error code list

How to reset / clear error codes on York furnaces

York tri-colour controls store up to five fault codes in memory, retained even if power is lost. Soft lockouts (on standard boards, the 6, 7 and 8 red-flash faults) reset automatically after one hour — the control keeps retrying hourly and resumes if the temporary condition, such as a gas-supply interruption, has cleared. Hard lockouts (for example the 11 red-flash blower-failure lockout, and the rollout fault on standard boards) do not restart on their own: fix the cause, then cycle power off and on at the furnace switch. A tripped rollout switch is a manual reset at the switch itself, and only after the rollout cause has been found. Clearing any lockout without fixing its cause just restarts the countdown to the next one.

How to diagnose any York 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.

Two York board generations, one LED: standard vs modulating tri-colour controls

Every Johnson Controls residential furnace manual in this check — from the older Unitary Products document 167808-UUM-A-1205 through the TG9S, TMLX and GF9S/GY9S manuals to the modulating TP9C and CM8M/YM8M manuals — uses the same physical reporter: one LED on the control board, visible through a clear view port in the blower door, able to flash red, green or amber. What changed between generations is not the light but the language it speaks, and the two languages disagree on real codes. The standard generation (single-stage and conventional two-stage families such as TG9S, TMLX and GF9S/GY9S) keeps amber simple: a slow amber flash means normal operation with a call for heat, a rapid amber flash warns of low flame sense current, and the only counted amber code is 4 amber flashes — a thermostat wiring alert (a 'Y' signal arriving without a 'G' signal). Its red list runs 1 to 11, with 6 red flashes meaning the pressure switch opened four times during one call for heat, and 10 red flashes meaning the gas valve is energised with no call for heat. The modulating generation (the Affinity-style modulating families, TP9C/YP9C and CM8M/YM8M among them) expands amber into a full status language — 1 amber for a cooling call, 2 for a heating call, 3 for the burner running on after the thermostat is satisfied, 4 and 5 for heating capacity reduced by circulating-air and combustion-air restrictions respectively, 6 for heat-pump heating — and it reassigns red codes: 6 red flashes becomes a modulating gas valve failure, 10 red flashes becomes a gas valve circuit shorted, 5 red flashes adds the auxiliary limit or condensate pressure switch to the rollout switch, 4 red flashes adds a defective temperature sensor and an open 24-volt fuse to the limit switch, and a 12th red code appears for a missing ID plug. Telling the generations apart is therefore a model question before it is a code question: modulating model families (the 9C and 8M designations in the manuals cited here) speak the second language, the conventional single-stage families speak the first, and the diagnostic chart printed inside your own blower door settles any doubt — photograph it. One warning belongs here: third-party websites also publish an older-looking single-red-LED table for York furnaces (1 flash as an ignition lockout, and so on). No Johnson Controls residential furnace manual found for this page defines that table, and a different 'heartbeat' flash table circulating online traces to JCI packaged rooftop units, not furnaces. Applying either to a residential York is how a pressure-switch fault gets 'fixed' as an ignition fault — identify the board first, then read the code.

Reading a York flash code correctly: colour, count, pause — and the stored history

A York flash code is three facts, and losing any one of them loses the code. The colour comes first: red is a fault, amber on a standard board is either a normal heat call (slow), a low flame-sense warning (rapid) or the single counted wiring alert, and green is the control's housekeeping voice. The count comes second, and it must be a full count: the LED flashes on and off at a fixed rate (a quarter second each way on some generations, a third of a second on others, while the slow normal-operation flash breathes at two seconds on and two seconds off), repeats the number that names the code, then rests for a two-second pause before repeating. Joining the pattern mid-cycle or counting through the pause manufactures codes that do not exist — watch at least three full repetitions, or video the LED and count from the recording. The third fact is that the code you see is not the only code the furnace remembers. York's controls store up to five fault codes and keep them through a power cut, and the board's LAST ERROR button plays them back, most recent first, with a two-second pause between codes: two green flashes answers 'nothing stored', and holding the button down for more than five seconds clears the memory, confirmed by three green flashes. York reserves that retrieval feature for a qualified service technician, and the reason is the same reason you should not clear codes casually — the history is evidence. It is also why a lockout should be read as a report, not a malfunction in itself. When a York control locks out, it is counting documented events: flame lost five times in one heating cycle (8 red flashes), ignition failed on three tries (7 red flashes), a limit open for more than five minutes (11 red flashes). Soft lockouts on standard boards retry automatically after one hour, which protects an empty house from a temporary gas interruption; hard lockouts wait for a human and a power cycle, because their causes — a dead blower, a tripped rollout — should be looked at, not waited out. So the correct reading discipline is: record the colour and the count, note what the furnace was doing when the code appeared, retrieve or note the stored history before resetting anything, and only then reach for the furnace switch. A reset erases the trail; the code was the trail.

Blink codes, display codes and lockouts

Two generations of fault reporting live side by side on modern furnaces. Older and simpler boards report through a single LED: a repeating count of flashes, read slowly against the chart printed inside the blower door — that chart, for your exact model, outranks any list on the internet, including this one. Newer communicating furnaces show alphanumeric codes (the E-series in the table above) and store a fault history a technician can scroll. Both generations share the lockout idea: after a set number of failed attempts at the same step — ignition is the classic — the board stops trying for a period (often an hour, or until power is cycled) instead of cycling forever against a fault that could overheat or flood the burners with unburned gas. A furnace in lockout is not broken by the lockout itself; it is a furnace that has already failed the same step repeatedly and is waiting for someone to find out why.

Furnace codes are also seasonal in a way washer codes are not. The first cold snap produces a wave of ignition and flame codes from furnaces that sat idle all summer — oxidised flame sensors, spider-nested burners, pressure-switch hoses holding condensate from the cooling season. Deep-winter adds frozen condensate lines on high-efficiency models and intake/exhaust terminations blocked by snow or ice, which present as pressure-switch codes. A code that appears once, on the coldest night of the year, and never again has often met its cause already; a code that appears every cycle, in any weather, is a component asking to be tested.

The most searched York furnace codes, in detail

2 red flashes — Pressure switch stuck closed

Two red flashes is York's vent-proof failing its first question, and the sequence explains why it comes first. On a call for heat, before starting the inducer, the control checks that the pressure switch is OPEN — at rest, with no draft, its normally open contacts must be open. Two flashes means they are already closed: the switch is claiming the vent is drafting before anything has moved air through it. The cycle therefore never begins — no inducer start, no ignition attempt — because a proving device that reports 'proved' unprompted cannot be trusted to report anything. Contrast its mirror, 3 red flashes, where the inducer runs and the switch never closes: 3 flashes accuses the vent path (blockage, hose, inducer), while 2 flashes accuses the switch side itself. York's manuals keep the cause list correspondingly short on both generations: a faulty pressure switch or miswiring; the modulating manuals (TP9C, CM8M/YM8M) add the pressure transducer to the check — 'Check pressure switch and pressure transducer' — because modulating controls read vent pressure through a transducer alongside the switch, and a transducer reporting pressure that is not there produces the same impossible-at-rest verdict. The welded-contact story is the physical archetype: contacts that have fused closed report closure forever, at rest and at work, and the control catches them at the one moment their lie is provable — before the inducer has any business making pressure. Miswiring tells the same lie electrically: a circuit made up wrong presents as permanently closed regardless of the switch's own state. Either way, York's standing prohibitions frame the whole entry: never bypass any safety control to allow furnace operation, and never adjust a pressure switch to make the furnace run. A furnace flashing 2 red has not lost its ability to heat; it has lost its witness that heating would be safe, and it declines to proceed without one.

Most likely cause: Faulty pressure switch — contacts stuck or welded closed — York's first-named cause on both generations. The switch's contacts have fused or its mechanism has stuck in the made position, so it reports closure at rest, under way, always. It is condemned by its state with the furnace at rest — no meter subtlety is required to catch a switch that is closed when nothing is running.

First check: SAFETY: this is a gas appliance whose vent proof has failed. Never jumper, bypass or adjust the pressure switch to get heat — York prohibits all three in its manuals. If you smell gas, stop and call a licensed HVAC technician (and the gas utility for a gas smell).

If it keeps coming back: A 2-flash code that returns intermittently — passing its at-rest check for days, then failing it — is a switch mechanism in decline: contacts sticking on a thermal or vibration schedule, or a transducer drifting on modulating models. A 2 that returns immediately after a switch replacement moves the diagnosis to the wiring or, on modulating boards, the transducer that was not tested. Record the pattern (cold starts only? after long runs? after service work?) — on this code the schedule is the diagnosis, because the fault itself is binary and brief.

3 red flashes — Pressure switch stuck open

Three red flashes is York's venting-proof failure, and the sequence explains it. On a call for heat the control first confirms the pressure switch is open (if it is already closed, that is 2 red flashes instead), then starts the inducer — the combustion blower that pulls exhaust through the heat exchanger and out the vent. The pressure switch must then close to prove the vent path is actually drafting. Three flashes means that proof never arrived: the inducer ran, but the switch stayed open. York's manuals name the suspects in the same breath on both board generations — a faulty inducer, a blocked vent pipe, a broken pressure switch hose or a faulty pressure switch; the modulating CM8M manual adds a blocked air intake pipe and a blocked condensate drain, and the standard TG9S manual adds disconnected pressure switch or inducer wires (its wiring-diagram summary compresses the whole code to 'Vent, intake, OR termination problem'). The switch is a safety proof, not a formality: it exists to stop the furnace firing into a blocked flue, which is why York's instructions also say, in plain words, never adjust a pressure switch to allow furnace operation, and never bypass any safety control. Treat 3 flashes as the furnace declining to light until its exhaust path is proven — the blockage is the fault, the switch is the messenger.

Most likely cause: Blocked vent, intake or termination — York's first family of causes and the TG9S summary's whole definition: a blocked vent pipe or air intake pipe, snow, ice, nests or debris at the outdoor terminations strangling the draft the switch has to sense.

First check: SAFETY: this is a gas appliance that has refused to prove its venting. Never jumper, bypass or adjust the pressure switch to get heat — York prohibits all three. If you smell gas, stop and call a licensed HVAC technician (and the gas utility for a gas smell).

If it keeps coming back: A 3-flash code that returns in deep cold points at termination icing or a condensate line that freezes; one that returns after rain points at water entering or sagging in the vent; one that returns on windy days points at termination placement or a marginal inducer. The weather pattern in your notes is the diagnosis — record when it happens, not just that it happened.

4 red flashes — Limit switch open

Four red flashes is York's overheating report, and on standard boards York defines it by one device: the main limit switch, a normally closed safety switch that opens when the air around the heat exchanger gets too hot and shuts the burners down while the control runs the blower and inducer to carry the heat away. The cause list is an airflow list, identical on both generations: dirty filter, improperly sized duct system, incorrect blower speed setting, incorrect firing rate, loose limit switch wiring or a faulty blower motor. The furnace is not overheating because it makes too much heat in the abstract — it overheats because too little air is moving over the heat exchanger to carry the heat into the house. York builds two escalations around this code, and both are documented behaviour, not damage: if the limit has not closed within five minutes, the standard-board control assumes the blower is not functioning, enters a hard lockout and starts flashing 11 red flashes instead; and if the main limit opens five times within a single call for heat, the control keeps flashing 4 red flashes but enters a one-hour soft lockout. The modulating generation widens the definition in a way that matters for diagnosis: its manuals (TP9C and CM8M) define four red flashes as 'high limit switch open or defective temperature sensor or 24 volt fuse is open', listing an open fuse on the control board among the causes — so on a modulating York, a dead low-voltage circuit can present as the limit code. That fuse branch is NOT in the standard boards' detailed definition (although the TG9S wiring-diagram summary table does flag 'Airflow problem OR open fuse' beside 4 Red), which is exactly why the board generation has to be identified before anyone orders parts.

Most likely cause: Dirty air filter — First on York's own cause list for this code on both generations. A loaded filter starves the heat exchanger of the air that is supposed to carry its heat away.

First check: SAFETY: this is a gas appliance reporting overheating. If you smell gas, see scorch marks, or hear banging or booming on ignition, turn the furnace off and call a licensed HVAC technician. Never bypass a limit switch to get heat — it is a fire guard.

If it keeps coming back: Four flashes that return after a filter change and open registers mean the restriction is deeper: a blower wheel matted with dust, a clogged evaporator coil above the furnace, collapsing duct liner, or a blower losing speed. On a modulating model, a 4-flash code that returns with a fresh fuse means the 24V short is still there. Each return trip is thermal stress on the heat exchanger — do not let limit trips become the furnace's normal operating cycle.

7 red flashes — Ignition lockout

Seven red flashes is the end of York's ignition arithmetic, not the beginning of it. On a call for heat the furnace runs its sequence — safeties proved, inducer drafting, pressure switch closed, igniter energised, gas valve opened — and attempts to establish flame. If flame cannot be established, it tries again; York's count is three tries in total (the standard manuals spell the arithmetic out: the no-light condition occurred 3 times — 2 retries — during the call for heat before locking out). After the third failure the control stops offering ignition and enters lockout, flashing 7 red flashes, for one hour; then, per both generations' manuals, it will try again to light. The cause list is the ignition chain itself, and the two generations divide it between them in a way worth preserving: the standard manuals (the GF9S/LC8V-era detailed text) name low gas pressure, a faulty gas valve, a faulty hot surface ignitor or a burner problem; the modulating TP9C manual compresses the same check to 'Check gas supply, ignitor, gas valve, flame sensor'; and the verified combined list adds what both support — gas valve off, a dirty or faulty flame sensor, and loose wires. Read as a system, the list walks the chain in order: fuel present (gas supply on, pressure adequate), fuel admitted (valve opens), fuel lit (hot surface ignitor hot and positioned), flame proved (sensor clean and reporting) and flame sustainable (burners clean enough to carry it). A 7-flash furnace has failed somewhere on that walk three times running, and the lockout is the control declining to keep opening a gas valve on an unproven burner. Distinguish its neighbours before diagnosing: 8 red flashes is flame ESTABLISHED and then lost five times in one cycle (a recycle lockout — different story, gas pressure/valve/sensor degradation mid-run), and a rapid amber flash is the low-flame-sense warning (below 1.5 microamps on standard boards, against a normal of about 3.7) that often precedes ignition trouble without locking anything out. Seven is specifically the never-lit lockout, and its one-hour retry is a mercy for transient causes — a gas supply restored, air in a reopened line purged — not a repair strategy.

Most likely cause: Low or no gas pressure — or the gas supply/valve off — First on the standard manuals' list (low gas pressure) and inside the modulating manual's 'check gas supply': a closed manual shut-off, the gas valve's own switch off after other work, an interrupted or sagging supply, or pressure too low to establish flame. The furnace cannot light gas it does not have, and York's sequence cannot distinguish 'no gas' from 'no ignition' until someone checks the supply.

First check: SAFETY: this is a gas appliance that has failed to light three times. If you smell gas at any point, stop — no further start attempts — and call the gas utility or a licensed HVAC technician. Never hold a gas valve open, jumper a safety, or keep power-cycling the furnace to harvest a light.

If it keeps coming back: A 7 that returns after the hourly retry, week after week, is a chain link degrading on a curve: an ignitor losing temperature season by season, a sensor coating faster than it is cleaned, gas pressure sagging only when every appliance in the house runs at once on the coldest nights. A 7 that returns only after gas or electrical work is a disturbed connection until proven otherwise. Each lockout is three unproved gas-valve openings; a furnace collecting them nightly is asking for the chain to be walked link by link, and the stored history's stack of 7s — read before anyone clears it — is the curve drawn in the furnace's own hand.

Deep-dive guides for the most searched codes

Related guides

Facts on this page were checked against manufacturer documentation: www.manualsdir.com · www.manualslib.com · manuals.plus · www.manualslib.com · www.manualsdir.com · www.manualsdir.com · manuals.plus