Knowledge base
Mitsubishi Electric fault codes
Ecodan • PUHZ
Mitsubishi Electric fault-code hub (Ecodan, PUHZ) — last verified 9 Sep 2026, reviewed by Ask Marcel team. Three sourced anchors: E6 = UI/UE communication (Ecodan range dependent); L5 = low water flow on Ecodan hydraulics; P8 = abnormal pipe temperature. Each article cites the model service manual — not interchangeable with Gree or Daikin definitions.
Mitsubishi Electric fault codes by product family
A code can mean different things depending on the range: open the sheet for the exact model.
L5 • Ecodan (Air/Eau)
Fault code L5 Mitsubishi Ecodan: Water flow fault
Specific to Ecodan air-to-water heat pumps, L5 indicates a water circulation anomaly. The heat exchanger temperature rises too quickly or the flow meter detects nothing.
E0
Fault code E0 Mitsubishi Electric: causes, diagnosis and solution
Fault code E0 indicates a signal transmission or reception anomaly between the remote controller(s) and the interface unit/flow temperature controller (FTC) of the outdoor unit, specifically when communication fails for 3 minutes for the main controller or 2 minutes for a secondary controller.
E9
Fault code E9 Mitsubishi Electric: causes, diagnosis and solution
Fault code E9 indicates a communication error (transmission error) between the indoor unit (unit interface/flow temperature controller) and the outdoor unit. This fault occurs when the outdoor unit continuously receives zeros after transmitting ones, or when it cannot find silence on the transmission path for 3 minutes.
EA
Fault code EA Mitsubishi Electric: causes, diagnosis and solution
Fault code EA indicates a wiring error or an excessive number of interface units/flow temperature control units connected to the outdoor unit. The outdoor unit control circuit detects the fault after 4 minutes of power supply.
EC
Fault code EC Mitsubishi Electric: causes, diagnosis and solution
Fault code EC indicates that the unit cannot complete the start-up process within 4 minutes of power-up. This results from a failed internal communication or signal disruption between units.
F5
Fault Code F5 Mitsubishi Electric: Causes, Diagnosis and Solution
Fault code F5 indicates that the circuit of the 63H connector (high-pressure switch) is open. This anomaly is detected if the circuit remains open for 3 consecutive minutes after power-up.
U1
Fault code U1 Mitsubishi Electric: causes, diagnosis and solution
Fault code U1 indicates abnormal high pressure detected during compressor operation, triggered by the opening of the high-pressure switch 63H (threshold at 4.15 MPa). This anomaly can result from hydraulic circuit problems, insufficient air circulation or electronic failures in the outdoor unit.
U2
Fault code U2 Mitsubishi Electric: causes, diagnosis and solution
Fault code U2 indicates an abnormally high discharge temperature (TH4 > 125°C or 110°C for 5 minutes) or an excessive compressor surface temperature (TH34 > 125°C). This anomaly stops the compressor to prevent damage, with a specific restart condition for the surface temperature.
U6
Fault Code U6 Mitsubishi Electric: Causes, Diagnosis and Solution
Fault code U6 indicates a power module anomaly detected during an overcurrent test (UF or UP), or a short circuit at the module output interface (IC700). It may also relate to a connection fault of the discharge and compressor surface thermistors.
U7
Fault code U7 Mitsubishi Electric: causes, diagnosis and solution
Fault code U7 indicates a superheat anomaly due to a discharge temperature that is too low. This fault is triggered when the discharge superheat remains at or below -15°C for 3 minutes, despite a minimum opening signal to the linear expansion valve after 10 minutes of compressor operation.
U8
Fault Code U8 Mitsubishi Electric: Causes, Diagnosis and Solution
Fault code U8 indicates an anomaly in the outdoor fan rotation speed during DC motor operation. This error is triggered if the rotation frequency is not detected according to specific thresholds related to the outdoor temperature.
U9
Fault code U9 Mitsubishi Electric: causes, diagnosis and solution
Fault code U9 on Mitsubishi Electric Ecodan HW140VHA2/YHA2 units indicates an input voltage anomaly or current sensor error, often related to a power synchronisation signal fault. This code can also appear when detecting overvoltage, undervoltage, L1 phase open, or an abnormal synchronisation signal.
UD
Fault code UD Mitsubishi Electric: causes, diagnosis and solution
Fault code Ud on Mitsubishi Electric Ecodan systems indicates overheating protection triggered when the liquid thermistor (TH3) or pressure sensor (63HS) detects a temperature of 70°C or higher during compressor operation.
UH
Fault code UH Mitsubishi Electric: causes, diagnosis and solution
Fault code UH indicates an abnormal current sensor reading or input current error detected by the system during compressor operation. This error occurs when the sensor detects an abnormal value, either between -1.0 A and 1.0 A, or an input current exceeding 40 A (or 37 A for 10 seconds).
Ed • Ecodan
Fault Code Ed Mitsubishi Ecodan: Hydrobox / Outdoor Unit Communication Error
On the Ecodan range, fault code Ed means the FTC hydrobox control board has lost communication with the outdoor unit.
P6
Fault Code P6 Mitsubishi Electric: Causes, Diagnosis and Solution
Fault code P6 indicates that the freeze or overheat protection of the plate heat exchanger has been activated. This code can relate to anti-freeze protection in cooling or heating mode, as well as anti-overheat protection in heating mode.
U3
Fault code U3 Mitsubishi Electric: causes, diagnosis and solution
Fault code U3 indicates an open circuit or short circuit detected on the discharge temperature thermistor (TH4) and/or the compressor surface thermistor (TH34) during compressor operation. Detection is inactive for the first 10 minutes of compressor start-up and during or after defrost.
U5 • Ecodan PUHZ-SW50VKA-BS
Fault code U5 Mitsubishi Electric: causes, diagnosis and solution
Fault code U5 indicates an abnormal heat sink temperature detected by thermistor TH8, exceeding model-specific thresholds (e.g., 77°C or 84°C). This signal may also originate from a voltage anomaly according to some manual references.
EB
Fault code EB Mitsubishi Electric: causes, diagnosis and solution
Fault code Eb indicates a poor connection (reversal or disconnection) of the cable linking the outdoor unit to the interface unit or flow temperature controller. The outdoor unit control board cannot assign the unit number to the interface within 4 minutes of power-up.
E8
Fault code E8 Mitsubishi Electric: causes, diagnosis and solution
Fault code E8 indicates a communication error (signal reception error) between the indoor unit (Interface unit/Flow temp. controller) and the outdoor unit. This fault is triggered when the outdoor unit receives no normal signal for a period of 3 minutes.
UE
Fault Code UE Mitsubishi Electric: Causes, Diagnosis and Solution
Fault code UE indicates abnormal pressure detected by the pressure sensor (63HS) when it registers 0.1 MPa or less. Detection is inactive for 3 minutes after compressor start and during or after defrost.