HeatingCodesFurnace not working? Decode the code.
Look up your furnace blinking light, tankless water heater error or mini-split code. We only list codes we could confirm in a manufacturer document, and we link the document on every page.
Popular code explanations
Carrier furnace status code 33: limit circuit fault
Carrier / Bryant gas furnaceCarrier furnace status code 34 (ignition proving failure) and code 14 (ignition lockout)
Trane / American Standard gas furnaceTrane furnace blinking 4 times: open temperature limit circuit
Rinnai tankless water heaterRinnai tankless water heater code 11: no ignition
Daikin ductless mini-splitDaikin mini-split error H6: position sensor abnormality (compressor start-up failure)
Navien tankless water heaterNavien tankless water heater error E110: abnormal air pressure
Browse code tables by equipment
Carrier and Bryant furnace status codes (5 furnace manuals compared)
16 codes from 5 manufacturer documents
Gas furnaceTrane furnace error codes: blinking lights and S9V2 / S9X display codes
38 codes from 3 manufacturer documents
Tankless water heaterRinnai tankless water heater diagnostic codes
40 verified codes
Tankless water heaterRheem tankless water heater error codes
34 verified codes
Tankless water heaterNavien NPN tankless water heater error codes
19 codes from 4 manufacturer documents
Commercial gas water heaterBradford White D-series (24 V Honeywell / ICON HD) error codes
19 verified codes
Ductless mini-splitMitsubishi Electric mini-split error codes
18 codes from 5 manufacturer documents
Ductless mini-splitDaikin mini-split error codes: FTXC, FTX-B, AXVJU and FTX-N/U series
37 codes from 4 manufacturer documents
Gas furnaceGoodman and Amana 96% furnace alarm codes
37 verified codes
Gas furnaceLennox furnace diagnostic codes (SL280DFV)
36 verified codes
Gas furnaceRheem and Ruud furnace fault codes (801T series)
17 verified codes
Gas furnaceYork TM9V furnace flash codes
19 verified codes
BoilerWeil-McLain Ultra boiler lockout codes
30 verified codes
Tankless water heaterTakagi tankless error codes (T-KJr2, T-K4, T-D2)
14 verified codes
Tankless water heaterNoritz tankless error codes
7 verified codes
Ductless mini-splitMitsubishi MSZ/MSY-GL blinking light codes
8 verified codes
Ductless mini-splitFujitsu wall-mounted mini-split error codes
32 verified codes
421 code entries in total. Tables state exactly which models each source covers.
Free tools
Fault code decoder
Search every verified code on the site by brand, code or symptom.
ToolHeating cost calculator
Compare natural gas, propane, oil, electric resistance and heat pump costs using EIA prices.
ToolRepair vs replace calculator
Apply ENERGY STAR and Department of Energy rules to your furnace, boiler or heat pump.
Winter heating guides
How to read your furnace blinking light code
GuideFurnace turns on and off every few minutes (short cycling): causes and safe checks
GuideFurnace igniter glows but the burners never light
GuideFurnace after a winter power outage: restart steps and generator safety
GuideTankless water heater no hot water in cold weather: what to check
GuideHeat pump in defrost mode: steam, noise and when to worry
How we keep this accurate
Many code lists online mix up brands or repeat each other. We do the opposite. Each code meaning on HeatingCodes was read in a manufacturer manual or an official source, the page links to that document, and the page says which models the document covers. If we could not confirm a code, we leave it out. For example, many sites call H6 a Mitsubishi code. We checked official fault tables in 12 Mitsubishi Electric and Mitsubishi Heavy Industries documents covering M-Series mini-splits, MXZ, P-Series, CITY MULTI, Ecodan and SRK-ZS units, and H6 was not listed as an error code in those tables. Daikin's service manuals do list it; our H6 page names the documents we checked and shows the Daikin sources.
Read more in our editorial policy and meet the editor.