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Fault code index · Sunsynk inverter and battery

Sunsynk Fault Code Index

Every Sunsynk fault code from the inverter display and SolarMan portal — what it means, the most likely cause, and what to do. Find your code in the index below or use the category sections to browse by system area.
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  • Sourced from official Sunsynk fault code document (v1.0)
  • Covers hybrid and battery-only models
  • SolarMan + inverter display codes
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How to find your fault code. Sunsynk fault codes appear on the inverter LCD display and in the SolarMan (formerly SolarmanPV) portal under Device > Status or in the alarm/event log. The code format is a short alphanumeric string or a description string (e.g. "Grid Lost", "Battery Low Voltage"). Share the exact code text from the screen or portal when booking.
Inverter faults

Fault codes generated by the Sunsynk inverter in response to DC overvoltage, temperature, or relay failures.

F01 / DC_Inversed_Failure PV polarity reversed
PV panels or string connected with reversed polarity — DC positive and negative cables swapped. Do not touch DC wiring. Requires engineer to check and correct DC string wiring. This is a safety fault; the inverter will not operate until corrected.
F02 / DC_Insulation_Failure Insulation fault
Insulation resistance between the DC circuit and earth is below the safe minimum. Common causes: damaged or degraded cable insulation, water ingress into a junction box or connector, or a faulty panel. Do not touch DC cabling. Requires engineer inspection and insulation resistance testing.
F03 / GFDI_Failure Ground fault / leakage current
Ground fault detector interrupt has tripped — excessive leakage current detected on the DC side. Can indicate a damaged panel, connector failure, or cable fault. Do not touch DC wiring. Requires engineer diagnosis.
F04 / GFDI_Ground_Failure Ground fault detected
Ground fault confirmed on DC circuit — current flowing through an unintended earth path. Closely related to F03; triggered when the GFDI relay confirms a persistent fault. Do not touch DC wiring. Requires engineer.
F05 / EEPROM_Read_FailureInternal memory fault
Inverter cannot read from its internal EEPROM memory — typically a hardware fault. Try a full power cycle (AC and DC off, wait 2 minutes). If the fault persists the inverter will require a service call or control board replacement.
F09 / IGBT_Failure Power module fault
The inverter's IGBT (insulated-gate bipolar transistor) power switching module has failed. This is a hardware fault requiring engineer attendance. The inverter will not operate. A power cycle is unlikely to resolve this — the unit typically requires workshop repair or replacement.
F13 / Working_Mode_changeWorking mode changed
The inverter has logged a change of working mode and briefly stopped — reported when the grid type or frequency setting is changed, when battery mode is set to 'No battery', or on older firmware whenever the work mode changes. Some Sunsynk documents list it as Grid_Mode_Changed. It normally clears by itself. If it stays on screen, a full power cycle (AC and DC off, wait one minute) usually clears it; if not, it is typically a settings-level issue that can be diagnosed remotely.
F23 / Tz_GFCI_OC_FaultTransient leakage current
The inverter detected a transient spike in leakage (earth-fault) current, usually originating from the PV side — a panel with an earth short, damaged cabling, or moisture. Switching events, lightning or grid disturbances can also trigger it as a one-off. Do not touch PV or DC cabling. Sunsynk's guidance is to restart the system two or three times; if the fault keeps returning, the array needs engineer leakage and insulation testing.
F24 / DC_Insulation_Fault PV insulation resistance low
Insulation resistance between the PV cables and earth is below the safe minimum — the inverter measures both PV cables against earth before connecting to the grid and reports F24 if either reads under 33kΩ. Distinct from F02 above: both insulation codes exist in the Sunsynk fault table, and F24 is the pre-connection impedance check. Usually a damaged DC cable, water ingress into a connector, or a faulty panel — often worse in damp or early-morning conditions, and noting that pattern helps diagnosis. Do not touch DC cabling. Requires engineer insulation resistance testing.
F26 / BusUnbalance_FaultDC busbar unbalanced
The two halves of the inverter's internal DC bus are unbalanced — reported in split-phase mode when the loads on the two output lines differ significantly. DC leakage current can also trigger it, and on a unit that keeps faulting a damaged IGBT or bus capacitor can be the underlying cause. Some Sunsynk documents spell it BusUnbalanced_Fault. Sunsynk's guidance is to restart the system two or three times; if it keeps returning, stop power cycling and get it diagnosed — a persistently unbalanced bus can damage the power module.
F64 / HeatSink_HighTemp_FaultInverter over temperature
Heatsink temperature too high. Check ventilation clearances — minimum 20cm from walls, not in direct sunlight, not enclosed in a sealed cabinet. Clear dust from heatsink vents. If ambient temperature is within range and vents are clear, the cooling fan or thermal sensor may be faulty.
Grid / G98 faults

Grid connection codes and events triggered by G98/G99 grid code settings. These are protection functions that disconnect the inverter during grid faults.

F35 / AC_NoUtility_FaultGrid absent / no AC supply
No AC grid detected — the inverter has lost its grid supply. Check the AC isolator and consumer unit main switch. If the mains supply is confirmed present at the distribution board, the AC wiring to the inverter or the internal grid relay may be faulty. The inverter reconnects automatically once grid is restored.
F43 / AC_VW_OverVolt_FaultGrid over voltage
Grid voltage above upper threshold. The inverter disconnects to protect itself and comply with G98/G99 requirements. Transient events reconnect automatically after 60–120 seconds. Recurring faults indicate a persistent high-voltage grid issue — contact your DNO.
F44 / AC_VW_UnderVolt_FaultGrid under voltage
Grid voltage below lower threshold. Check AC isolator and connections. If grid voltage is confirmed low from the DNO supply, contact your network operator. Transient dips reconnect automatically.
F47 / AC_OverFreq_FaultOver-frequency disconnect
Grid frequency above limit (typically above 51Hz in the UK). Transient; the inverter disconnects and reconnects automatically when frequency returns to range. Frequent occurrences should be reported to the DNO.
F48 / AC_UnderFreq_FaultUnder-frequency disconnect
Grid frequency below limit (typically below 47Hz in the UK). Transient; the inverter reconnects automatically once frequency recovers. Frequent occurrences should be reported to the DNO.
Grid code faultGrid code mismatch
Inverter grid code setting does not match region. The Sunsynk must be set to UK grid code (G98/G99). Requires installer-level access on the inverter LCD to reconfigure.
Battery faults

Fault codes related to battery voltage, BMS communication, and battery protection events.

F56 / DC_Bus_Bar_Voltage_Too_LowBattery / DC bus voltage low
DC bus voltage is too low — one of the most common Sunsynk faults in the UK. Usually caused by the battery being fully depleted or the BMS shutting down after a protection event. Ensure the battery is switched on and the DC breaker between inverter and battery is closed. Allow a charge cycle. If voltage doesn't recover, BMS protection may have latched — a full power cycle (battery off at isolator, wait 60 seconds, back on) is often required.
F55 / DC_VoltHigh_FaultDC bus voltage high
The inverter's internal DC bus voltage is above its safe maximum — the high-side twin of F56 above, and distinct from F54 below, which is over voltage at the battery terminals. Most commonly the requested charge voltage is set above the battery pack's own high-voltage alarm threshold (a frequent mismatch with third-party or self-managed BMS batteries), the PV input voltage is outside the permitted range, or — less often — a bus capacitor has failed internally. It typically appears near full charge, so note the battery voltage and state of charge shown when it trips. Do not adjust BMS or charge-voltage settings yourself — charge settings can often be checked remotely, but a recurring fault can also be internal hardware.
F54 / BAT_HighVolt_FaultBattery over voltage
Battery voltage above safe maximum. The BMS will typically disconnect the battery in this state. Do not attempt further charging. Contact Sunsynk support — this may indicate a BMS calibration issue or a cell imbalance fault.
F58 / BMS_Comm_FaultBMS communication lost
Inverter has lost communication with the battery BMS. Check CAN or RS485 communication cable between inverter and battery — a loose connector is the most common cause. Power cycle inverter and battery (off, wait 60 seconds). Check firmware versions are compatible. If the fault returns after a successful power cycle, the cable or BMS port may be faulty.
F20 / Tz_Dc_OverCurr_FaultDC over current trip
The hardware-level DC overcurrent protection has tripped — current on the battery or PV side exceeded the limit. Usually the battery cannot deliver the current the inverter demanded: a battery C-rating or BMS discharge limit too small for the inverter, a large load starting while running on battery, the maximum discharge current set wrongly, or undersized battery cables. Overcurrent from the PV side can also trigger it. Shown as HW_DC_OverCurrent_Fault on some firmware. Reduce the load, then power cycle (DC and AC off, wait one minute). If it returns, the discharge settings and cable sizing need professional checking against the inverter's demands — do not change current settings yourself.
Battery over currentCurrent exceeded BMS limit
Charge or discharge current exceeds BMS limit. May indicate a cell imbalance or BMS fault. Requires engineer.
EPS / backup faults

Fault codes related to EPS (Emergency Power Supply) backup function.

EPS over loadLoad exceeds EPS rating
Load on EPS backup circuit exceeds inverter EPS rating. Remove high-draw appliances from backup circuit. EPS circuit is typically rated at 3–6kW — not suitable for cookers, electric showers, or EV chargers.
F34 / AC_Overload_FaultBackup load over rating
The load on the inverter's backup/load (UPS) terminal exceeds the permitted power range — this is the F-code Sunsynk units display for the EPS overload condition described above. Some Sunsynk documents also label it AC Overcurrent fault. Usually too much running on the essential circuit at once — showers, kettles, heaters or EV chargers on a circuit sized for essentials — though an incorrectly selected grid mode can also contribute. Work out what was running when it tripped, move high-draw appliances off the backup circuit, then restart. If it trips on genuinely modest loads, the backup circuit design needs engineer review.
F18 / Tz_Ac_OverCurr_FaultAC over current / load surge
The hardware-level AC overcurrent protection has tripped — a surge of current on the load side exceeded the inverter's limit. Sunsynk describes it as an overload on the Load terminal and notes it is quite a common fault. Shown as HW_AC_OverCurrent_Fault on some firmware. Typically a heavy surge from motor-driven appliances starting (pumps, compressors, air conditioning) or many loads switching on at the same moment. Note whether it coincides with a particular appliance starting, reduce what runs on the backup circuit, and restart. If it recurs with modest loads and no obvious surge source, it needs engineer diagnosis — do not alter any wiring yourself.
EPS under voltageOutput voltage low
EPS output voltage collapsed, usually due to overload or a wiring fault on the EPS circuit. Check backup circuit wiring and reduce load.
Communication faults

Faults related to data communication between inverter and monitoring portal, and with system components.

F29 / Parallel_CANBus_FaultParallel communication fault
On systems with more than one Sunsynk inverter connected in parallel, the units have lost communication with each other over the parallel CAN cable — Sunsynk's troubleshooting guidance describes it as a very common fault on parallel installations. One Sunsynk manual's code table lists F29 under a different name, AC_AirSwitch_Fault, but the parallel communication meaning is the one the official troubleshooting documents use. It also appears normally during parallel-system start-up and clears once all inverters are on. Only relevant with two or more inverters: check every unit is switched on first; if the fault persists, the cable, parallel addresses and termination resistor settings need installer-level checking — the configuration side can often be reviewed remotely.
W04 / Meter_Comm_FailMeter offline
Inverter cannot communicate with the export meter (RS485 meter) or cannot read the CT clamp. Check meter cable connections at both the inverter and meter ends. If using a CT clamp, confirm it is correctly clamped around the incoming supply cable and the cable is intact.
W05 / CT_Wrong_Direction_WarnCT clamp reversed
CT clamp is installed facing the wrong direction. This causes the inverter to misread import and export — it may export when it should import, or vice versa, resulting in wasted energy or grid export when battery should be charging. The CT clamp must be rotated 180° to face toward the consumer unit. Requires engineer correction.
SolarMan data gapPortal not receiving data
Portal shows no data. Check WiFi logger (WLAN-Logger or similar) LED — flashing indicates WiFi disconnection. Reconfigure WiFi via the SolarMan app if needed.
Code not listed here?

Sunsynk releases firmware updates that may introduce new fault codes. If your code isn't listed, share the exact code from your inverter display or SolarMan and we'll identify it.

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Full diagnostic guides by fault type
F02 · DC insulation fault
DC insulation fault

Identifying the fault source: cabling, connectors, or panel junction box.

BMS communication lost
Battery communication fault

CAN/RS485 cable checks, power cycle, firmware compatibility, and hardware fault diagnosis.

Grid code fault · F35 / F43 / F44
Grid code and grid faults

G98/G99 grid code configuration and recurring grid trip diagnosis.

FAQ

Sunsynk fault code questions

Sunsynk fault codes appear on the inverter LCD display and in the SolarMan (formerly SolarmanPV) portal under Device > Status or in the alarm/event log. The SolarMan app shows the fault history including timestamps. Note the exact fault code or description text — including the F-code number if shown — before contacting support.
A BMS communication lost fault means the inverter has stopped receiving data from the battery management system. This is commonly caused by a loose or disconnected CAN or RS485 cable between the inverter and battery, a firmware version mismatch, or a BMS fault state after a protection event. Try a full power cycle (inverter and battery off, wait 60 seconds) as a first step. If the fault returns, check cable connections and contact support with the exact fault code.
A grid code fault usually means the inverter's grid code setting doesn't match the local grid requirements. In the UK, Sunsynk inverters must be configured for G98 (systems ≤3.68kW) or G99 (systems >3.68kW). An incorrect grid code setting can cause the inverter to trip off repeatedly. This setting requires a qualified installer or engineer to change — it is not accessible to end users.
Some Sunsynk fault codes triggered during power cuts are temporary and clear once the grid returns. If the code persists after grid restoration, a free remote diagnostic (no fix, no fee) can determine whether there's an underlying issue with your EPS or battery configuration.
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