What does Daikin error code U4 mean on a VRV system?

U4 on Daikin VRV and split systems indicates a transmission fault between the indoor and outdoor units over the F1/F2 communication bus. The outdoor PCB has stopped hearing the indoor (or vice versa) past the timeout window. Check the F1/F2 interconnect wiring for breaks, shorts, or reversed polarity; confirm there is no 230 V on the communication pair (which destroys both PCBs); verify every indoor unit has a unique address; and re-seat both ends of the cable. Power-cycle both units together for 30 seconds before condemning a board.

How do I read Daikin error codes without a remote controller?

On Daikin split outdoor units, the diagnostic LED on the outdoor PCB blinks fault codes that you decode using the model-specific flash table in the service manual. On VRV outdoor units, the seven-segment readout near the main PCB shows the active code directly; press the BS1 (MODE) button to cycle through stored faults. For older units without a display, short the TEST/CHECK pins on the service connector and count the LED sequence. The Daikin Service Checker (Type III) or Service Tool software via a laptop reads codes over the H-link bus on commercial units.

What causes Daikin error code E7 on split systems?

E7 indicates an outdoor fan motor fault. The fan-motor driver detects abnormal rotation feedback or no commutation pulses. Common causes: a seized or restricted fan blade, a failed Hall-effect or feedback sensor inside a DC inverter motor, a blown fan-motor IPM/driver PCB, or a damaged motor capacitor on older AC-driven units. Verify the fan blade spins freely by hand, measure winding resistance phase-to-phase (should be balanced within ten percent), inspect the motor driver board for burnt components, and confirm the motor connector is fully seated. Replace the motor or driver board as a paired set on inverter units.

How do I clear error codes on a Daikin VRV IV outdoor unit?

Active faults clear automatically once the underlying condition resolves and the unit re-communicates. To clear stored fault history on VRV IV, use the BRC1E/BRC1H remote controller: enter the Service Menu, navigate to Error History, and select Clear. From the outdoor unit itself, press and hold BS3 (RETURN) for five seconds while in the standard service mode. Safety faults that latched on a physical switch (high-pressure switch trip from F6/E3, drain pump float on A3) require a manual reset at the device before the controller will restart the compressor. Power-cycling alone does not clear latched safety faults.

What is Daikin error code L4 and how do I fix it?

L4 indicates the inverter radiation fin (heatsink) temperature has exceeded the safety limit, typically around 90 to 95 degrees Celsius. The inverter PCB throttles or stops the compressor to protect the IGBTs. Clean the outdoor coil and inverter cooling fins, confirm the condenser fan ramps to full speed under load, and verify airflow is not recirculating into the inlet. Check that the inverter heatsink thermistor reads correctly (open or shorted thermistors falsely report high temperature). On high-ambient sites, confirm the unit is within its published operating envelope; rooftop installations behind parapets often suffer L4 from heat soak.

What does Daikin error H6 mean and how do I diagnose it?

H6 indicates a position-detection sensor malfunction on the inverter compressor: the inverter PCB cannot confirm the compressor rotor angle, so it cannot commutate the IPM safely. Causes include a stalled or mechanically locked compressor, an open winding, a failed Hall-effect or shunt sensor in the inverter module, or a wiring fault between the inverter PCB and the compressor terminals. Measure compressor winding resistance phase-to-phase (should be balanced and non-zero), check insulation to ground above one megohm, and verify the inverter PCB outputs balanced PWM under starting load. A hard-locked compressor is the most common root cause.

What triggers Daikin code A3 on split and ducted systems?

A3 indicates the drain level control system has tripped: the drain pump float switch has detected high water in the condensate pan or the pump has failed to clear it within the time limit. Verify the condensate drain line is clear (P-trap not dry, no biofilm or algae blockage), confirm the drain pump runs on demand, check the float switch is free and not jammed by debris, and inspect the pump check-valve. Wet floors below an indoor unit usually appear minutes before A3 latches the unit off. On systems with ducted cassettes, ensure the unit is mounted level so the drain flows toward the pump pickup.

How do Daikin Altherma heat-pump fault codes differ from VRV codes?

Altherma heat pumps share the two-character fault format but add hydronic-specific codes for water-side faults: 7H flags low water flow (check the strainer, circulator pump, and air bleed), AA covers electric backup heater overtemperature, U7 reports a backup-heater contactor fault, and 8H flags abnormal water temperature. Refrigerant-side codes (E3, E4, F3, F6) read the same as on VRV. The Altherma user interface shows only the active code; full fault history is available via the Daikin Service Monitor connected to the H-link port on the indoor module. Treat Altherma as an air-to-water VRV with extra hydronic safeties layered on top.

What does U2 mean on a Daikin outdoor unit?

U2 indicates a power-supply voltage abnormality at the outdoor unit: line voltage is out of range, a phase is missing on three-phase systems, or the inverter DC-bus capacitors have detected over- or under-voltage. Measure incoming line voltage at the disconnect (must be within plus or minus ten percent of the rated value), confirm all three phases are present and balanced on commercial units, inspect the inrush-current resistor on the inverter PCB (often charred when capacitors fail), and check the DC-bus capacitor voltage with a meter rated for at least 450 V DC. Brownouts and voltage sags from nearby loads frequently trigger transient U2 events that clear on power-cycle.

What is Daikin error code L5 and what causes it?

L5 indicates an instantaneous overcurrent on the inverter DC output: the inverter PCB has detected a current spike to the compressor that exceeded the IGBT short-circuit threshold, and the IPM has shut down to protect itself. Causes include a shorted compressor winding, a shorted IGBT module on the inverter PCB, liquid slugging on startup (refrigerant migrated to the compressor sump during a long off cycle), or a wiring short between the inverter and compressor terminals. Megger the compressor windings to ground, measure phase-to-phase resistance for balance, and inspect the inverter board for visible IGBT damage. L5 after compressor replacement usually points to a damaged inverter board, not the new compressor.

Quick Answer

Daikin systems display two-character fault codes on the indoor controller and outdoor PCB seven-segment readout. Letter prefixes group the fault domain: A-codes flag indoor-unit faults, C-codes mark thermistor failures, E/F-codes signal outdoor-unit and refrigerant problems, H/J/L-codes cover compressor and inverter faults, and U-codes report communication or power-supply issues. AskWhiz indexes every published Daikin code.

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By Octavian Ghindea

Co-founder & CTO · Reviewed May 2026

What error codes does Daikin display?

Transmission disruption between indoor and outdoor unit — check F1/F2 communication wiring

Suction air thermistor malfunction — measure NTC resistance and check connector seating

Position detection sensor malfunction on inverter compressor — verify winding balance and insulation

Drain level control system tripped — clear drain line and check pump and float switch

High pressure / freeze-up protection activated — inspect coil, airflow, and refrigerant charge

Inverter instantaneous overcurrent — megger compressor and inspect IGBT module

Outdoor unit fan motor malfunction — check motor windings and driver PCB

Inverter radiation fin overtemperature — clean coil and confirm condenser fan operation

Discharge pipe high temperature — verify charge level and check for restricted condenser airflow

Power supply voltage defect — measure incoming line voltage and DC-bus capacitors

Common questions about Daikin equipment

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