Home/HVAC & Water Heater Error Codes
HVAC & Water Heater Error Codes
Find what the code on your mini-split, heat pump, gas furnace or water heater means. We cover 321 codes across 12 brands. Every entry is taken from the manufacturer's own manual or service document, says which model series it applies to, and links to that document.
Codes change between model series. The same code can mean different things on two units from the same brand, so check the series listed with each code. Your unit's own manual is the final word. Reviewed October 2026.
344 codes (showing 60, type to narrow it down)
Mitsubishi Electric P1Intake (room) sensor errorPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric P2Pipe (liquid) sensor errorPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric P9Pipe (condenser/evaporator) sensor errorPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric E6Indoor/outdoor unit communication errorPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric P4Float switch connector openPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric P5Drain pump error (water leakage abnormality)PLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric PAForced compressor stopPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric P6Freezing or overheating protection operationPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric EECommunication error between indoor and outdoor unitsPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric P8Pipe temperature errorPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric E4Remote controller signal receiving errorPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric FbIndoor unit control system errorPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric PLRefrigerant circuit abnormalPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric E1Remote controller control board errorPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric E0Remote controller transmission errorPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric E9Indoor/outdoor communication error (transmitting)PLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric UPCompressor overcurrent interruptionPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric U3Outdoor unit thermistor open or shortPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric UFCompressor overcurrent (compressor locked)PLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric U2High discharge temperature or insufficient refrigerantPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric U1Abnormal high pressure or overheating protectionPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric U5Abnormal heat sink temperaturePLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric U8Outdoor unit fan protection stopPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric U6Compressor overcurrent or power module abnormalPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric U7Superheat abnormality (low discharge temperature)PLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric U9Overvoltage, voltage shortage or current sensor errorPLA-RP35/50/60/71/100/125/140BA ceiling cassette indoor units (Mr. Slim, OCH416 service manual)Mitsubishi Electric Lamp blinks 0.5 s on/offMiswiring or serial signal errorMSZ-AP15VG / MSZ-AP20VG wall-mounted indoor units (OBH838 service manual)Mitsubishi Electric 2 blinksIndoor coil or room temperature thermistor errorMSZ-AP15VG / MSZ-AP20VG wall-mounted indoor units (OBH838 service manual)Mitsubishi Electric 3 blinksIndoor fan motor errorMSZ-AP15VG / MSZ-AP20VG wall-mounted indoor units (OBH838 service manual)Mitsubishi Electric 4 blinksIndoor control system errorMSZ-AP15VG / MSZ-AP20VG wall-mounted indoor units (OBH838 service manual)Mitsubishi Electric 5 blinksOutdoor power system abnormalityMSZ-AP15VG / MSZ-AP20VG wall-mounted indoor units (OBH838 service manual)Mitsubishi Electric 6 blinksOutdoor thermistor errorMSZ-AP15VG / MSZ-AP20VG wall-mounted indoor units (OBH838 service manual)Mitsubishi Electric 7 blinksOutdoor control system errorMSZ-AP15VG / MSZ-AP20VG wall-mounted indoor units (OBH838 service manual)Mitsubishi Electric 14 or more blinksOther abnormalityMSZ-AP15VG / MSZ-AP20VG wall-mounted indoor units (OBH838 service manual)Daikin A1Indoor unit PCB abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin A5Freeze-up or heating peak-cut protectionDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin A6Indoor fan motor abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin C4Indoor heat exchanger thermistor abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin C9Room temperature thermistor abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin U0Refrigerant shortageDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin U2Low-voltage or over-voltage detectionDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin U4Signal error between indoor and outdoor unitDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin UAUnspecified voltage between indoor and outdoor unitDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin E1Outdoor unit PCB abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin E5Compressor overload (OL) activationDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin E6Compressor lockDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin E7Outdoor DC fan lockDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin E8Input overcurrent detectionDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin EAFour-way valve abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin F3Discharge pipe temperature controlDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin F6High pressure control in coolingDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin H0Compressor system sensor abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin H6Compressor position sensor abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin H9Outdoor temperature thermistor abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin J3Discharge pipe thermistor abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin J6Outdoor heat exchanger thermistor abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin L3Electrical box temperature riseDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin L4Radiation fin temperature riseDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin L5Output overcurrent detectionDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)Daikin P4Radiation fin thermistor abnormalityDaikin FTXS-L / FDXS-L inverter pair ductless series (09 to 36 class, models FTXS09-36LVJU, FDXS09-12LVJU)
Mini-splits and heat pumps
Gas furnaces
Tankless and tank water heaters
✅ Usually fine to keep running · 🧭 Check a few things first · 🛑 Turn it off and call a licensed pro
🛑 Stop and call a licensed pro if
- You smell gas. Leave the house, do not touch switches, and call your gas utility from outside.
- Flame rollout, limit or pressure switch codes that come back after one reset.
- Anything involving the control board, gas valve, flame sensor, igniter or venting.
- A carbon monoxide alarm sounds. Get everyone outside and call 911 or the fire department.
Shaun Cain · Certified HVAC & Refrigeration Technician · Ask an HVAC technician