Furnace Fault Codes

What your furnace's blinking light or error code actually means

Most furnaces report faults by flashing a status LED a set number of times, or by showing a code on a small display. Each entry below explains what a given signal means, what normally causes it, what you can safely check yourself, and when it needs a licensed technician.

Before you look up a code anywhere. A furnace fault code is not a standard, and it is not standard within a brand either — four of the six biggest manufacturers publish code lists that disagree with each other. Which list applies to your furnace is usually the first thing to settle.

First, check it is actually a fault

A blinking light is not automatically a problem — every brand uses the same light to say the furnace is running normally. The patterns that mean nothing is wrong lists every one of them.

Start with what the furnace is doing

If you have not got a code out of it yet, these describe the behaviour and list every code that produces it.

Do not know the brand? Start with the count

The flashes mean different things on different furnaces, so the count on its own is not an answer — but these pages show every meaning side by side, which is usually enough to recognise the right one.

Start with your manufacturer

Goodman and Amana furnace fault codes — 80 codes (also Amana)
Carrier, Bryant and Payne furnace status codes — 15 codes (also Bryant, Payne)
Trane and American Standard furnace flash codes — 34 codes (also American Standard)
Lennox furnace alert codes — 61 codes
York, Luxaire and Coleman furnace flash codes — 25 codes (also Luxaire, Coleman)
Rheem, Ruud and Weather King furnace blink codes — 10 codes (also Ruud, Weather King)
Heil, Tempstar and Comfortmaker furnace codes — 15 codes (also Tempstar, Comfortmaker, Arcoaire, KeepRite)
Armstrong Air, AirEase, Concord and Ducane furnace codes — 16 codes (also AirEase, Concord, Ducane)

By part

The same part produces several different codes, and several different brands word them differently. These pages collect every code that points at one component.

Pressure switch — Furnace pressure switch codes on every brand
High limit switch — Furnace high limit switch codes by brand
Flame sensor — Furnace flame sensor codes on every brand
Rollout switch — Furnace rollout switch codes: why it tripped
Hot surface igniter — Furnace igniter fault codes by manufacturer
Inducer / draft motor — Furnace inducer motor fault codes by brand
Indoor blower motor — Furnace blower motor fault codes by brand
Gas valve — Furnace gas valve fault codes by manufacturer
Grounding and line polarity — Furnace grounding and reversed polarity codes
Voltage and fuse — Furnace voltage and fuse codes by brand

Goodman and Amana

1 flash — Lockout after too many failed ignition attempts
2 flashes — Pressure switch is closed when it should be open
3 flashes — Pressure switch will not close
4 flashes — High limit switch is open — the furnace is overheating
5 flashes — Flame detected when no flame should be present
6 flashes — Rollout switch has tripped
7 flashes — Flame signal is too weak
8 flashes — Igniter circuit fault, most often caused by poor grounding
9 flashes — High stage pressure switch stuck open
rapid flashing — Reversed 115 volt polarity, a grounding problem, or an open igniter circuit
LED off — No power to the furnace, or an internal control fault
continuous on — Normal operation — no fault stored
6 flashes — Rollout limit open, or control module fuse blown

Goodman and Amana display codes

E0 — Lockout after too many failed ignition attempts
E1 — Low stage pressure switch closed at the start of the heating cycle
E2 — Low stage pressure switch stuck open
E3 — High limit switch is open — the furnace is overheating
E4 — Flame detected when no flame should be present
E5 — Low voltage fuse is open
E6 — Flame signal is too weak
E7 — Igniter fault or improper grounding
E8 — High stage pressure switch closed at the start of the heating cycle
E9 — High stage pressure switch stuck open
EA — Reversed 115 volt polarity
Ed — Rollout switch has tripped
EC — Inducer motor overcurrent
EF — Auxiliary switch or input is open

Goodman and Amana blower codes

b0 — Blower motor is not running
b1 — Blower communication error
b2 — Blower motor horsepower mismatch
b3 — Blower motor operating at a power, temperature, or speed limit
b4 — Blower motor current trip or lost rotor
b5 — Blower motor locked rotor
b6 — Blower motor over or under voltage trip, or over temperature trip
b7 — Incomplete parameters sent to the motor
b9 — Low indoor airflow
d0 — Data not yet on network
d4 — Invalid memory card data

Carrier and Bryant

Status code 11 — No previous code stored
Status code 12 — Blower running after power up
Status code 13 — Limit circuit lockout
Status code 14 — Ignition lockout
Status code 21 — Gas heating lockout — will not reset automatically
Status code 22 — Abnormal flame-proving signal — flame detected with the gas valve closed
Status code 23 — Pressure switch did not open
Status code 24 — Secondary voltage fuse is open
Status code 31 — Pressure switch did not close, or reopened
Status code 33 — Limit circuit fault — a limit or flame rollout switch is open
Status code 34 — Ignition proving failure
Status code 45 — Control circuitry lockout
LED continuously off — No power reaching the control
LED rapid flashing — Line voltage polarity reversed
Status code retrieval, amber LED controls — How to read stored status codes on Carrier amber LED boards

Trane and American Standard

2 flashes — System lockout — retries or recycles exceeded
3 flashes — Draft pressure error
4 flashes — Open high limit device
5 flashes — Flame sensed when no flame should be present
6 flashes — 115 volt AC power reversed, or poor grounding
7 flashes — Gas valve circuit error
8 flashes — Low flame sense signal
9 flashes — Ignitor circuit problem, or low voltage between neutral and 24 volt common
Flashing slow — Normal — no call for heat
Flashing fast — Normal — call for heat
Continuous on — Replace the integrated furnace control
Continuous off — Check power

Rheem, Ruud and Weather King

1 blink — Soft lockout, one hour
2 blinks — Pressure switch failure — switch remains open
3 blinks — Limit switch open
4 blinks — Pressure switch failure — switch remains closed
5 blinks — Twinning circuit failure

Goodman GMEC96 and Amana AMEC96 colour codes

1 red flash — Flame sensed when no flame should be present
2 red flashes — Pressure switch stuck closed, or an inducer error
3 red flashes — First stage pressure switch stuck open, or an inducer error
3 double red flashes — Second stage pressure switch stuck open, or an inducer error
4 red flashes — Open limit switch
5 red flashes — Open rollout switch, or open fuse detected
6 red flashes — Pressure switch cycle lockout
7 red flashes — External lockout — ignition retries exhausted
8 red flashes — External lockout — recycles exhausted
9 red flashes — Grounding problem or reversed polarity
10 red flashes — Gas flow detected with a call for heat
11 red flashes — Limit switch open due to blower failure
12 red flashes — Ignitor relay failure
rapid amber flashing — Low flame sense current
rapid red flashing — Twinning error
solid red — Internal control fault, gas valve error, microprocessor or frequency check failure
3 amber flashes — Second stage heat called with no first stage call
4 amber flashes — Cooling called with no fan call
1 amber flash — Normal operation — first stage heat
solid green — Standby — powered, no call
2 amber flashes — Normal operation — second stage heat
1 green flash — Normal operation — low stage cooling
2 green flashes — Normal operation — high stage or single stage cooling
rapid green flashing — Normal operation — fan only, no heating or cooling

Lennox communicating alert codes

Alert code 200 — Rollout limit switch open
Alert code 204 — Check gas valve
Alert code 205 — Gas valve relay contact closed
Alert code 206 — Gas valve second stage relay fault
Alert code 207 — Hot surface igniter sensed open
Alert code 223 — Low pressure switch open
Alert code 226 — High pressure switch stuck closed
Alert code 227 — Low pressure switch open in run mode
Alert code 228 — Inducer calibration issue
Alert code 229 — Ignition on high fire — information only
Alert code 240 — Low flame current in run mode
Alert code 241 — Flame out of sequence — still present
Alert code 250 — Primary limit switch open
Alert code 252 — Discharge air temperature high
Alert code 270 — Flame failed to ignite — Watchguard
Alert code 271 — Low pressure switch open — Watchguard
Alert code 272 — Low pressure switch open in run mode — Watchguard
Alert code 273 — Flame failed in run mode — Watchguard
Alert code 274 — Primary limit switch open more than three minutes — Watchguard
Alert code 201 — Indoor blower motor communication lost
Alert code 202 — Blower motor and unit size mismatch
Alert code 203 — Invalid or unset unit size code
Alert code 275 — Flame out of sequence — Watchguard
Alert code 276 — Furnace calibration failure, or high pressure switch fault
Alert code 290 — Ignition circuit fault — Watchguard
Alert code 291 — Heating airflow below minimum — Watchguard
Alert code 292 — Indoor blower motor will not start — Watchguard
Alert code 294 — Inducer motor overcurrent — Watchguard
Alert code 370 — Interlock switch open — no 24 volts at the DS terminal
Alert code 116 — High 24 volt secondary voltage
Alert code 117 — Poor earth ground on the reporting unit
Alert code 224 — Low pressure switch stuck closed
Alert code 225 — High pressure switch will not close
Alert code 295 — Indoor blower motor overheating
Alert code 344 — Y1 relay stuck on the furnace control
Alert code 349 — O to R jumper cut on the furnace control

York, Luxaire and Coleman

Fault code retrieval — How to read and clear stored fault codes on York UTEC boards
Green heartbeat — Normal operation, no call for heat, no active errors
Amber heartbeat — Normal operation with a call for heat
1 red flash — Flame sensed with the gas valve off
3 red flashes — Pressure switch open, or first stage pressure switch open
3 double red flashes — Second stage pressure switch stuck open
5 red flashes — Open rollout switch
6 red flashes — Pressure switch cycle lockout
7 red flashes — One hour lockout after ignition retries
8 red flashes — Lockout on recycles, flame dropouts
9 red flashes — Grounding, reversed polarity, or reversed transformer leads
10 red flashes — Gas valve energised with no call for heat
11 red flashes — Limit switch open more than five minutes — blower failure
12 red flashes — Open hot surface igniter
Rapid red flashing — Twinning error or incorrect 24 volt phasing
Rapid amber flashing — Low flame sense current
Solid LED — Control fault detected
Steady off — No power to the board, or control failure
2 red flashes — Pressure switch stuck closed, or an inducer error
4 red flashes — Open high limit switch
3 amber flashes — Second stage heat present with no first stage call
4 amber flashes — Cooling called with no fan call
2 amber flashes — Normal operation with a call for second stage heat
Which York control board you have — York used two control board generations with different code meanings
1 amber flash — Normal operation with a call for heat, Emerson boards

Reading the codes

Reading a furnace fault code — How to find, count, and interpret the diagnostic light before looking anything up
When to stop and call someone — The furnace conditions that are not a diagnosis problem
The same code means different things — Four of the six biggest furnace brands publish more than one code list

Goodman modulating display codes

IF — Internal control fault
Ft — Field test mode
On — Normal operation
F — Continuous fan
A — Airflow display, followed by the CFM value
H — Gas heat demand, followed by the demand percentage
HI — High heat at 100 per cent demand
LO — Low stage heat
dF — Defrost demand
P1 — Low stage compressor, heating mode
P2 — High stage compressor, heating mode
C1 — Low stage compressor, cooling mode
C2 — High stage compressor, cooling mode
C — Compressor cooling with a single stage compressor
P — Compressor heating with a single stage compressor
d — Dehumidification cooling with a single stage compressor
d1 — Dehumidification, low stage cooling, communicating mode
d2 — Dehumidification, high stage cooling, communicating mode

Heil, Tempstar and Comfortmaker

Which diagnostic system you have — Heil, Tempstar and Comfortmaker furnaces use two different code systems that contradict each other
Heartbeat — Normal operation — standby or a call for heat
LED off — The control is not powered
1 flash — Not used — if you are counting one flash, count again
2 flashes — Low pressure switch closed when it should be open
3 flashes — Low pressure switch still open 30 seconds after the inducer started
4 flashes — Limit switch string is open
5 flashes — Flame sensed out of sequence — flame signal still present
6 + 1 flashes — Soft lockout — failed to light within four trials for ignition
6 + 2 flashes — Soft lockout — flame lost during run, cycling pressure switch, or blocked condensate
6 + 3 flashes — Soft lockout — airflow proving circuit opened during the run
6 + 4 flashes — Soft lockout — limit circuit opened during the run
7 flashes — Soft lockout — limit trips taking longer than two minutes to reset
8 flashes — High pressure switch closed when it should be open
9 flashes — High pressure switch open when it should be closed

Armstrong Air, AirEase, Concord and Ducane

Heartbeat — Control powered, no errors detected
Error code recall — The last ten faults, retained even through a power cut
LED off — No power to the control, or a control hardware fault
1 flash — Reverse line voltage polarity
2 flashes — Improper earth ground
3 flashes — Burner failed to light, or lost flame during a heat demand
4 flashes — Low flame signal — check the flame sensor
5 flashes — Watchguard — burner failed to light, retries or recycles exceeded
7 flashes — Primary or secondary limit open, or Watchguard after three minutes open
8 flashes — Rollout switch open
9 flashes — Pressure switch failed to close, or opened during a heat demand
10 flashes — Watchguard — pressure switch opened five times during one heat demand
11 flashes — Pressure switch stuck closed before the inducer started
12 flashes — Flame sensed without the gas valve energised
13 flashes — Low line voltage
6 flashes — Not used — if you are counting six flashes, count again

Rheem condensing furnace blink codes

Which blink code list applies — Rheem publishes two blink code lists that contradict each other
1 blink — Limit circuit is open
2 blinks — Pressure switch did not close within 10 seconds
3 blinks — Pressure switch closed when it should be open
4 blinks — Lockout after five failed ignition attempts

Lennox seven-segment diagnostic codes

Which Lennox code list applies — Lennox uses two code systems, and knowing which you are reading matters
E200 — Hard lockout — rollout circuit open
E204 — Gas valve mis-wired
E223 — Pressure switch failed open
E224 — Pressure switch failed closed
E227 — Pressure switch opened during ignition or run
E240 — Low flame current in run mode
E241 — Flame sensed out of sequence — flame still present
E250 — Limit switch circuit open
E290 — Ignitor circuit fault — failed ignitor or triggering circuit
E270 — Soft lockout — retries exceeded, no flame current sensed
E271 — Soft lockout — retries exceeded, pressure switch opened
E272 — Soft lockout — recycles exceeded, pressure switch opened
E273 — Soft lockout — recycles exceeded after flame failure
E274 — Soft lockout — recycles exceeded, limit circuit opened
E275 — Soft lockout — flame sensed out of sequence, signal now gone
E110 — Low line voltage
E111 — Line voltage polarity reversed
E112 — Ground not detected — system shuts down
E113 — High line voltage
E114 — Line voltage frequency out of range
E115 — Low 24 volt supply
E117 — Poor ground detected — warning only
E106 — Twin communication fault
E163 — Furnace control board failure

Trane and American Standard seven-segment codes

Which Trane code system you have — Trane furnaces use either flash codes or a seven-segment display, and they share no numbering
E2.1 — Retry exceeded — flame never sensed, one hour lockout
E2.2 — Recycles exceeded — flame sensed then lost, one hour lockout
E3.2 — Open pressure switch, first stage
E3.4 — Open pressure switch, second stage
E04 — Open limit — thermal, rollout, or reverse airflow switch
E05 — Flame detected when it should not be present
E6.1 — Line voltage polarity reversed
E6.2 — Bad grounding
E6.3 — Igniter relay failed, or igniter open
E08 — Flame current low but still usable
E09 — Open inducer limit switch or condensate pressure switch
E01 — Internal control failure
E2.3 — First stage gas valve not energised when it should be, ten times
E3.1 — Shorted pressure switch, first stage
E3.3 — Shorted pressure switch, second stage
E7.1 — First stage gas valve energised when it should be off
E11 — Gas valve relay faults — five conditions in one code
E12 — Open fuse
E17 — Blower motor not responding to communication
E18 — Blower communication failure on the control
IdL, Xt1, Xt2, aRF and the other status codes — Normal operation — the display is not showing a fault

This site is a reference, not a substitute for a licensed HVAC technician. Gas appliances can leak carbon monoxide and cause fire. Anything involving gas lines, the heat exchanger, or the flame sensing circuit should be handled by a licensed professional. Pages are written with AI assistance from the sources listed on each page and checked against them before publishing.