Mitsubishi Electric Error Codes & Diagnostics
Complete diagnostic directory for official Mitsubishi Electric fault codes. Verify root causes, safe troubleshooting steps, and replacement part numbers before calling a technician.
Mitsubishi Electric E6 error code: indoor to outdoor communication fault
Mitsubishi Electric assigns E6 to a communication error between the indoor and outdoor units, detected on the indoor side. The two ends have stopped exchanging their signal over the connecting cable, so the code identifies a broken conversation rather than a specific failed board. Applies to: Mitsubishi Electric M-Series and Mr Slim systems that publish the E-series communication table This meaning follows Mitsubishi Electric literature for the M-Series and Mr Slim families that publish an E-series table with E6 and E7. Mitsubishi Heavy Industries and other brands assign these characters differently, so confirm both model numbers before applying this page. Owner-safe checks: With the system off at the isolator, check for any obvious damage to the visible run of interconnecting cable and confirm no recent storm, outage, or rodent activity. | Record when E6 started, whether it followed any install or electrical work, and whether the outdoor fan turns while the code is shown. Qualified technician: Inspecting the S1, S2, S3 terminals, testing conductor continuity, and checking the board communication circuits all require isolating power and belong with a qualified technician.
Ecodan L9: three different flow faults share one code
L9 means the control has measured low flow in a primary water circuit. The manual lists it three times for three circuits: heat source side sensed by the flow sensor, then Zone1 and Zone2, each sensed by a flow switch. The digit shown in Request code 569 under Running information tells you which of the three it is. It reports a measurement, not a failed pump. Applies to: Ecodan FTC5 cylinder units, EHPT20X-MHCW and EHST20(D)(C)-MHCW Scoped to the FTC5 controller as documented in the EHPT20X-MHCW and EHST20(D)(C)-MHCW cylinder service manual. Later FTC generations and the newer Ecodan ranges carry their own code tables, and a code letter shared between two controllers is not a shared meaning. Owner-safe checks: Read the fault code and then look up Request code 569 in Running information on the main controller, and write down the digit shown. | Photograph the outdoor unit model number on the data plate, since the recommended flow range is per model. | Note the system pressure on the gauge and whether the pressure has been falling, since a leak is on the manufacturer's cause list. | Record whether the code appears at start-up or during steady running, and whether the circuit has been opened recently. | Check that no radiator valve or zone valve has been closed off since the system last ran normally. Qualified technician: Strainer cleaning, purging a sealed system, and any work that breaks into the water circuit belong to the installer or a qualified heating engineer. | Electrical testing of the flow sensor, the flow switch, the CN1A connector, and the IN2, IN3, and IN7 terminals is technician work on a live control. | DIP switch settings on the FTC board are commissioning parameters, and changing one without knowing which circuits exist can hide the fault rather than clear it. | Replacing or resizing the circulation pump is a design decision about system head, not a parts swap.
Mitsubishi P1: the room sensor the whole control loop depends on
P1 reports that the indoor intake air thermistor is reading outside the range the control accepts, which the reference describes as an open circuit, a short circuit, or a detached connector. The reading matters because the intake air sensor is what the system calls room temperature, so once it is untrusted the control has no basis for deciding capacity and stops rather than guessing. Applies to: Mitsubishi Electric indoor units that publish the P-series fault table, covering Mr Slim and M-Series indoor equipment This reading covers Mitsubishi Electric indoor families that publish the P-series fault table. Mitsubishi Heavy Industries equipment is a separate manufacturer with its own table, and a P1 shown by a third-party controller wired to a Mitsubishi indoor unit is not the same entry. Confirm the indoor model code before acting on it. Owner-safe checks: Compare the room temperature the controller displays with a separate thermometer placed near the indoor unit intake, and write both values down. | Confirm the front panel and filters are fully seated and closed, since a partly open panel changes what the intake sensor is exposed to. | Record the blink pattern or controller display, the indoor address, and whether the fault follows any recent maintenance. Qualified technician: Measuring thermistor resistance, inspecting board connectors, and replacing a sensor harness require the indoor electrical enclosure to be opened by a qualified technician. | If P1 is accompanied by a burning smell, visible discoloration, or a tripping circuit protective device, isolate the unit and stop using it until it has been inspected.
Mitsubishi P2: the pipe sensor that tells defrost and freeze control what to do
P2 identifies an abnormality in the indoor pipe temperature thermistor, the sensor clamped to the indoor heat exchanger rather than the one reading room air. Its value drives freeze protection in cooling and heat-exchanger temperature logic in heating, so the control stops rather than run those functions blind. Applies to: Mitsubishi Electric indoor units publishing the P-series fault table, including M-Series wall units and Mr Slim indoor equipment The entry read here belongs to Mitsubishi Electric indoor units that publish the P-series table. Some Mitsubishi indoor units carry more than one pipe thermistor, and the table then separates them by code, so the position of the failed sensor comes from the service manual for that exact indoor model rather than from the code alone. Owner-safe checks: Switch the affected indoor unit to fan only if the coil has visible frost, and let it thaw without heat, tools, or water. | Note the indoor address, the room, and whether other heads on the same system continue to work normally. | Write down any period in the preceding weeks when heating airflow was slow to start or cooling produced indoor frost. Qualified technician: Verifying sensor mounting, measuring thermistor resistance against the published curve, and inspecting the indoor harness all need the indoor casing opened by a qualified technician. | Repeated indoor coil frosting alongside P2 needs refrigerant and airflow assessment, which is licensed work and not an owner task.
Mitsubishi P5: the drain protection stopped the unit before water did
P5 is a drain protection stop on a Mitsubishi Electric indoor unit. The control saw the float switch rise, or it saw the drain pump circuit fail to respond, and it shut cooling down to keep the condensate tray from overflowing. The code proves water did not leave the tray fast enough. It does not name the blockage, the pump, or the switch as the failed part. Applies to: Mitsubishi Electric indoor units that publish the P-series protection table, including Mr Slim cassette, ducted, and ceiling-suspended indoor units P5 is read here from the Mitsubishi Electric fault-code reference for the indoor families that publish the P-series table. Wall-mounted units without a condensate pump do not carry the same detection, and a Mitsubishi Electric controller fitted to another manufacturer's indoor unit will not follow this table. Match the code to the indoor unit model on its own rating label rather than to the outdoor unit. Owner-safe checks: Switch the indoor unit to fan only or off so the coil stops producing condensate, and leave it that way until the fault is assessed. | Look at the visible outdoor end of the condensate line during a period when the unit had been cooling, and note whether any water discharged. | Photograph the controller showing P5 together with the indoor unit address, and note the outdoor temperature and humidity at the time. Qualified technician: Checking the float switch, testing the drain pump circuit, and clearing a condensate line inside the indoor unit require the electrical enclosure to be opened, which is qualified service work. | Water staining on a ceiling, a wall, or an electrical accessory near the unit is a stop condition. Isolate the indoor unit and arrange service rather than running it to see whether the code returns.
Mitsubishi Electric P6 error code: coil freeze or overheat protection
Mitsubishi Electric assigns P6 to a freezing or overheating protection trip at the indoor coil. In cooling the coil pipe temperature fell far enough to risk ice, and in heating it climbed too high, so the control stopped the compressor. It points at airflow across the coil, the coil thermistor, or the refrigerant condition rather than at one named part. Applies to: Mitsubishi Electric Mr Slim and M-Series systems that publish the P-series protection table This reading follows Mitsubishi Electric literature for the Mr Slim and M-Series families that publish a P-series protection table. Other Mitsubishi Electric ranges, and Mitsubishi Heavy Industries equipment, use different code tables, so match the indoor and outdoor model numbers first. Owner-safe checks: With the system off, remove and clean the indoor filters, dry them fully, refit them, and confirm nothing blocks the intake or outlet of the indoor unit. | Note whether P6 happened in cooling or heating, whether the coil was frosted, and whether airflow felt weak beforehand. Qualified technician: Checking refrigerant charge, cleaning the indoor coil or blower wheel, and measuring or replacing the coil thermistor require a qualified technician with gauges.
Mitsubishi Electric P8 fault: what the code actually narrows down
Mitsubishi Electric P8 reports an abnormal piping-temperature relationship. It can follow low refrigerant flow, a restricted circuit, a displaced or faulty thermistor, or crossed piping and wiring on some multi systems; P8 does not identify one failed part. Applies to: Mr Slim families covered by Mitsubishi Electric's P8 reference This interpretation is limited to Mitsubishi Electric systems included in the cited P8 reference. It does not apply to Mitsubishi Heavy Industries equipment, and the exact service sequence must be selected by the complete indoor and outdoor model numbers. Owner-safe checks: Photograph the full code and both model plates, then record the mode and elapsed run time when P8 returns. Qualified technician: Refrigerant measurements, thermistor testing, terminal checks, and correction of paired piping or wiring belong to qualified service personnel.
Mitsubishi U2: high discharge temperature is a charge question, not a compressor verdict
U2 is an outdoor protection stop raised when the compressor discharge temperature rises beyond the limit the control allows, a condition the reference also ties to refrigerant shortage. High discharge temperature is what a compressor does when it has too little refrigerant returning to cool it, so the code is a symptom of the refrigerant circuit rather than proof the compressor is damaged. Applies to: Mitsubishi Electric outdoor units publishing the U-series fault table, including M-Series and MXZ multi-zone outdoor equipment This applies to Mitsubishi Electric outdoor units that publish the U-series table. The same two characters appear on other manufacturers with unrelated meanings, and Mitsubishi Heavy Industries is a separate company with its own code set. Take the reading from the outdoor unit model plate, not from the brand name on the indoor grille. Owner-safe checks: Turn the system off at the controller and leave it off, since repeated restarts run the compressor under the condition that triggered the limit. | Walk the visible line set and the outdoor unit looking for oil film, frost patches, or a disturbed insulation run, and photograph anything you find. | Write down how the system had been performing over the preceding weeks and the outdoor conditions when it stopped. Qualified technician: Measuring charge, searching for a leak, recovering refrigerant, and testing the discharge thermistor are certified refrigerant-handling activities under EPA Section 608 in the United States and F-Gas rules in the United Kingdom and Europe. | Do not add refrigerant, tighten a flare, or operate the system to see whether the code stays away. Running a compressor at high discharge temperature is what the protection exists to prevent.
Mitsubishi U6: the inverter cut the compressor current before anything melted
U6 is raised when the outdoor inverter detects compressor current or power module conditions outside the range it will drive. It is an electrical protection acting in milliseconds, which is why the code arrives as an abrupt stop rather than a gradual loss of output. The detection names the current, not the cause of the current. Applies to: Mitsubishi Electric inverter outdoor units publishing the U-series fault table, including M-Series single-zone and MXZ multi-zone equipment The entry described here belongs to Mitsubishi Electric outdoor units publishing the U-series table. Multi-zone outdoor units serving several indoor heads report the code centrally, so the address shown does not identify a room. Confirm the outdoor model from its plate before applying this reading. Owner-safe checks: Attempt at most one restart from the controller, then stop and note how long the outdoor unit ran before the code returned. | Check whether other appliances on the property are behaving normally and whether any protective device in the consumer unit or panel has operated. | Leave the isolator on and the operation off for several hours before any further attempt if the system has been unused for a long period. Qualified technician: Measuring compressor winding resistance, drive output, and supply voltage under load requires opening an energised outdoor enclosure and is qualified work. | A burning smell, visible scorching, or a protective device that trips when the unit starts is a stop condition. Isolate at the dedicated switch and arrange service without further attempts.