Fox ESS Inverter Error Codes List and Troubleshooting

Updated 6 September 2026 · By SolarNevs Research Desk, Dealer surveys + verified sources · 1 source · Method ↗

Illuminated display screen and status panel on a wall-mounted solar inverter. — SolarNevs spec card

Key Takeaways

Fox ESS inverters display text-based alarms for issues with the grid, battery, PV array, or internal components.
Many faults can be resolved by checking external connections or performing a full power cycle of the system.
Always disconnect all power sources (AC, DC PV, battery) and wait at least 5 minutes before inspecting internal wiring.
For internal hardware faults or persistent issues, contact a qualified technician or your Fox ESS supplier.

What do Fox ESS inverter error codes mean?

Fox ESS inverters display text-based error codes on their LCD to indicate operational issues. These codes point to specific problems with the grid, battery, PV array, or internal components, requiring systematic troubleshooting. Understanding these messages is the first step to resolving system disruptions and restoring normal operation.

Diagnosis

When your Fox ESS inverter displays an error code, follow these general diagnostic steps before attempting specific fixes:

Note the Exact Error Message: Write down the full text of the error code displayed on your inverter's LCD. This is crucial for accurate troubleshooting.
Check Inverter Status Lights: Observe any LED indicators on the inverter. Their color and pattern can provide additional diagnostic information.
Inspect External Connections: Visually check all external wiring for your system:

- AC Grid Connection: Ensure the main grid breaker is on and AC cables are securely terminated.
- PV Array DC Connections: Verify that PV string cables are properly connected and the DC isolator switch is in the "ON" position.
- Battery Connections: Confirm battery cables are tight and the battery's DC breaker or switch is on. Check communication cables between the battery and inverter.
- Meter/CT Connections: If applicable, ensure the energy meter or CT clamp is correctly wired and oriented.

Perform a Full System Power Cycle (Safely):

- WARNING: Risk of severe injury or death from electric shock and arc flash. High-voltage lithium battery strings (Mira, ECS, EP) operate between 85VDC and 600VDC, posing severe direct current electrical shock and arc flash risks. Internal DC bus capacitors store lethal electrical energy.
- Turn OFF the AC grid isolator / breaker on the distribution board.
- Turn OFF the high-voltage DC battery isolator / breaker.
- Turn OFF the PV array DC isolator switch on the inverter underside.
- Wait at least 5 minutes for internal high-voltage capacitors to fully bleed down until the LCD and all LED indicators are completely unlit. This is a critical safety step to avoid electric shock.
- Attempting unauthorized repairs or opening the inverter enclosure (beyond specified access points for wiring) may void your Standard 5-Year manufacturer warranty on hybrid inverters and lithium storage batteries through authorized Pakistani distributors (e.g., SunSolar, BatteryMAX). If unsure, contact a qualified technician.
- Power up the Battery System First: Turn ON the battery DC breaker, then press and hold the Master BMS power switch for 2–3 seconds until the green LED turns solid and internal contactors click.
- Turn ON the PV DC isolator switch.
- Turn ON the AC grid isolator.
- Monitor the inverter's display for the error to clear.

Consult the Error Code Table: Use the detailed table below to match your specific error message with its meaning and recommended fix.

WARNING: Any 'Fix' instruction in the table below that involves checking or manipulating physical wiring, connections, or internal components (e.g., DIP switches) MUST be performed ONLY after following the complete safety shutdown procedure detailed in the 'Perform a Full System Power Cycle (Safely)' section above. Failure to adhere to these safety protocols poses a severe risk of electric shock and arc flash, and may void your product warranty.

Fox ESS Inverter Error Code Table

Symptom detail	Likely cause	Fix
Grid Lost Fault	Grid is lost.	System will reconnect if the utility is back to normal. Or seek help from us, if not go back to normal state.
Grid Volt Fault	Grid voltage out of range.	System will reconnect if the utility is back to normal. Or seek help from us, if not go back to normal state.
Grid Freq Fault	Grid frequency out of range.	System will reconnect if the utility is back to normal. Or seek help from us, if not go back to normal state.
10min Volt Fault	The grid voltage is out of range for the last 10 Minutes.	System will reconnect if the utility is back to normal. Or seek help from us, if not go back to normal state.
SW Inv Cur Fault	Output current high detected by software.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
DCI Fault	DC component is out of limit in output current.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
HW Inv Cur Fault	Output current high detected by hardware.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
SW Bus Vol Fault	Bus voltage out of range detected by software.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Bat Volt Fault	Battery voltage fault.	Check if the battery input voltage is within the normal range. Or seek help from us.
SW Bat Cur Fault	Battery current high detected by software.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Iso Fault	The isolation is failed.	(See Safety Warning above table) Please check if the insulation of electric wires is damaged. Wait for a while to check if back to normal. Or seek for help from us.
Res Cur Fault	The residual current is high.	Please check if the insulation of electric wires is damaged. Wait for a while to check if back to normal. Or seek for help from us.
Pv Volt Fault	PV voltage out of range.	Please check the output voltage of PV panels. Or seek for help from us.
SW Pv Cur Fault	PV input current high detected by software.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Temp Fault	The inverter temperature is high.	Please check if the environment temperature. Wait for a while to check if back to normal. Or seek for help from us.
Ground Fault	The ground connection is failed.	(See Safety Warning above table) Check the voltage of neutral and PE. Check AC wiring. Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Over Load Fault	Over load in on grid mode.	Please check if the load power exceeds the limit. Or seek for help from us.
Eps Over Load	Over load in off grid mode.	Please check if the eps load power exceeds the limit. Or seek for help from us.
Bat Power Low	The battery power is low.	Wait the battery to be recharged. Or seek for help from us.
HW Bus Vol Fault	Bus voltage out of range detected by hardware.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
HW Pv Cur Fault	PV input current high detected by hardware.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
HW Bat Cur Fault	Battery current high detected by hardware.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
SCI Fault	The communication between master and manager is fail.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
MDSP SPI Fault	The communication between master and slave is fail.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
MDSP Smpl Fault	The master sample detection circuit is failed.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Res Cur HW Fault	Residual current detection device is failed.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Inv EEPROM Fault	The inverter eeprom is fault.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
PvCon Dir Fault	The PV connection is reversed.	(See Safety Warning above table) Check if the positive pole and negative pole of PV are correctly connected. Or seek help from us.
Bat Relay Open	The battery relay keeps open.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Bat Relay Short Circuit	The battery relay keeps close.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Bat Buck Fault	The battery buck circuit mosfet is fail.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Bat Boost Fault	The battery boost circuit mosfet is fail.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Eps Relay Fault	The eps relay is failed.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
BatCon Dir Fault	The battery connection is reversed.	(See Safety Warning above table) Check if the positive pole and negative pole of battery are correctly connected. Or seek help from us.
Main Relay Open	The grid relay keeps open.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
S1 Close Fault	The grid relay S1 keep close.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
S2 Close Fault	The grid relay S2 keep close.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
M1 Close Fault	The grid relay M1 keep close.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
M2 Close Fault	The grid relay M2 keep close.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
GridV Cons Fault	The grid voltage sample value between master and slave is not consistent.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
GridF Cons Fault	The grid frequency sample value between master and slave is not consistent.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Dci Cons Fault	The dci sample value between master and slave is not consistent.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Rc Cons Fault	The residual current sample value between master and slave is not consistent.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
RDSP SPI Fault	The communication between master and slave is fail.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
RDSP Smpl Fault	The slave sample detection circuit is failed.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
ARM EEPROM Fault	The manager eeprom is fault.	Disconnect PV, grid and battery, then reconnect. Or seek help from us, if not go back to normal state.
Meter Lost Fault	The communication between meter and Inverter is interrupted.	(See Safety Warning above table) Check if the communication cable between meter and Inverter is correctly and well connected.
BMS Lost	The communication between BMS and Inverter is interrupted.	(See Safety Warning above table) Check if the communication cable between BMS and Inverter is correctly and well connected.
Bms Ext Fault	The communication between BMS and Inverter is interrupted.	(See Safety Warning above table) Check if the communication cable between BMS and Inverter is correctly and well connected.
Bms Int Fault	DIP switch at the wrong position; The communication between battery packs is interrupted.	(See Safety Warning above table) Move the DIP switch to the correct position; Check if the communication cable between battery packs is correctly and well connected.
Bms Volt High	Battery over voltage.	Please contact battery supplier.
Bms Volt Low	Battery under voltage.	Please contact battery supplier.
Bms ChgCur High	Battery charge over current.	Please contact battery supplier.
Bms DchgCur High	Battery discharge over current.	Please contact battery supplier.
Bms Temp High	Battery over temperature.	Please contact battery supplier.
Bms Temp Low	Battery under temperature.	Please contact battery supplier.
BmsCellImbalance	The capacities of cells are different.	Please contact battery supplier.
Bms HW Protect	Battery hardware under protection.	Please contact battery supplier.
BmsCircuit Fault	Bms hardware circuit fault.	Please contact battery supplier.
Bms Insul Fault	Battery insulation fault.	Please contact battery supplier.
BmsVoltsSen Fault	Battery voltage sensor fault.	Please contact battery supplier.
BmsTempSen Fault	Battery temperature sensor fault.	Please contact battery supplier.
BmsCurSen Fault	Battery current sensor fault.	Please contact battery supplier.
Bms Relay Fault	Battery relay fault.	Please contact battery supplier.
Bms Type Unmatch	The capacity of battery packs is different.	Please contact battery supplier.
Bms Ver Unmatch	The software between slaves are different.	Please contact battery supplier.
Bms Mfg Unmatch	The cell manufacture is different.	Please contact battery supplier.
Bms SwHw Unmatch	The slave software and hardware are not match.	Please contact battery supplier.
Bms M&S Unmatch	The software between Master and Slave are not match.	Please contact battery supplier.
Bms ChgReq NoAck	No action for charging request.	Please contact battery supplier.

Understanding Fox ESS Alarm Types

Fox ESS inverters, particularly the H1(G2)/AC1(G2) and H1-G2-WL series, communicate issues using clear, text-based alarm strings on their display. Unlike some other brands that rely on numeric codes, Fox ESS aims to provide a direct description of the problem. This article focuses on these text alarms as they are directly attested in the official manuals we checked.

Common categories of faults include:

Grid-Related Faults: These errors, such as Grid Lost Fault, Grid Volt Fault, Grid Freq Fault, and 10min Volt Fault, indicate problems with the utility grid connection. They often resolve automatically when grid conditions stabilize. For persistent grid overvoltage issues in Pakistan, you may need to adjust inverter settings like Volt-Watt response mode or check AC cable sizing. Learn more about solar inverter grid overvoltage errors in Pakistan.
Battery-Related Faults: Messages like Bat Volt Fault, Bat Power Low, BMS Lost, or various Bms prefix faults (e.g., Bms Volt High, Bms Temp Low, BmsCellImbalance) point to issues with your battery system. BMS Lost specifically indicates a communication interruption between the inverter and the battery's Battery Management System (BMS). For battery communication issues, refer to our guide on lithium battery inverter compatibility errors and BMS fixes.
PV Array Faults: Errors such as Pv Volt Fault, SW Pv Cur Fault, HW Pv Cur Fault, and PvCon Dir Fault relate to the solar panel input. PvCon Dir Fault is a critical warning indicating reversed polarity in your PV wiring.
Internal Inverter Faults: Many alarms, including SW Inv Cur Fault, DCI Fault, Temp Fault, SCI Fault, and Inv EEPROM Fault, signal internal hardware or software malfunctions within the inverter itself. These often require a full system power cycle as a first step.
Communication Faults: Meter Lost Fault and BMS Lost are specific communication errors. Meter Lost Fault means the inverter cannot communicate with the external energy meter, which is crucial for features like zero-export limiting. Ensure the communication cables are correctly and securely connected.

For a broader understanding of inverter errors, consult our inverter error code glossary. If your inverter shows an error but no output, our general guide on inverter shows error but no output can provide further troubleshooting steps.

Safety: High-Voltage Systems Require Caution

Working with solar inverters and battery systems involves significant electrical hazards. Fox ESS inverters operate with high DC voltages from both the PV array and the battery, posing severe risks of electric shock and arc flash.

High-Voltage DC Shock Hazard: PV open-circuit voltages reach up to 600VDC on single-phase H1/KH models and up to 1000VDC on three-phase H3-Pro series. High-voltage lithium battery strings (Mira, ECS, EP) operate between 85VDC and 600VDC, posing severe direct current electrical shock and arc flash risks.
Mandatory 5-Minute Capacitor Discharge Delay: Internal DC bus capacitors store lethal electrical energy. Electricians must wait at least 5 minutes after fully disconnecting AC grid, DC PV isolator, and battery switches before opening wiring covers or servicing terminals. The manual states: "Wait 5 min before you open the upper lid or the DC lid."
Proper Grounding: Ensure the inverter and all associated components are correctly grounded according to local electrical codes. A Ground Fault indicates a critical safety issue with the grounding connection.

When to call a technician instead

While many common Fox ESS inverter errors can be resolved with basic troubleshooting, certain situations require professional intervention:

Persistent Internal Faults: If errors like SCI Fault, MDSP SPI Fault, Inv EEPROM Fault, or any HW (hardware) fault persist after a full power cycle, it indicates an internal component failure. These require specialized diagnostic tools and expertise.
Battery Management System (BMS) Faults: For Bms prefix faults (e.g., Bms Volt High, Bms Temp Low, BmsCircuit Fault, Bms Relay Fault), the recommended action is to "Please contact battery supplier." These indicate issues within the battery's internal management system that cannot be user-repaired.
Isolation or Residual Current Faults: Iso Fault and Res Cur Fault indicate serious electrical insulation problems that could pose a safety risk. A qualified electrician should investigate and repair these immediately.
Warranty Concerns: Attempting unauthorized repairs or opening the inverter enclosure (beyond specified access points for wiring) may void your Standard 5-Year manufacturer warranty on hybrid inverters and lithium storage batteries through authorized Pakistani distributors (e.g., SunSolar, BatteryMAX).
Lack of Expertise or Tools: If you are unsure about any troubleshooting step, do not have the necessary safety equipment, or lack experience with high-voltage electrical systems, it is always safer to call a certified solar technician.

For any issues that fall outside simple external checks or power cycling, contact your Fox ESS installer or an authorized service center.

Frequently asked questions

What does 'Grid Lost Fault' mean on my Fox ESS inverter?

A 'Grid Lost Fault' indicates that your Fox ESS inverter has detected zero utility AC voltage, meaning the grid connection is lost. The system will reconnect if the utility is back to normal. Or seek help from us, if not go back to normal state.

How do I fix a 'Bat Volt Fault' on my Fox ESS inverter?

A 'Bat Volt Fault' indicates a battery voltage fault, meaning the battery input voltage is outside its normal operating range. You should check if the battery input voltage is within the normal range. Or seek help from us.

What causes a 'Meter Lost Fault' on a Fox ESS inverter?

A 'Meter Lost Fault' occurs when the inverter cannot communicate with the external energy meter. This is typically caused by an incorrectly or poorly connected communication cable between the meter and the Inverter.

What should I do if my Fox ESS inverter shows an 'Iso Fault'?

An 'Iso Fault' indicates that the isolation is failed. WARNING: Before checking electrical wiring, you MUST safely shut down your entire system: turn OFF the AC grid, DC PV, and battery isolators, and wait at least 5 minutes for capacitors to discharge. Failure to do so poses a severe risk of electric shock. Attempting unauthorized repairs or opening the inverter enclosure (beyond specified access points for wiring) may void your Standard 5-Year manufacturer warranty on hybrid inverters and lithium storage batteries through authorized Pakistani distributors (e.g., SunSolar, BatteryMAX). You should then check if the insulation of electric wires is damaged. Wait for a while to check if back to normal. Or seek for help from us.

Why does my Fox ESS inverter display 'Temp Fault'?

A 'Temp Fault' means the inverter temperature is high. Please check if the environment temperature. Wait for a while to check if back to normal. Or seek for help from us.

References

H1(G2)/AC1(G2) SERIES User Manual — accessed 23 August 2026