Fault Code Reference

FoxESS Fault Codes

FoxESS hybrid inverters and battery systems. Popular across UK installations covering H1, H3, and ECS series inverters with AC-coupled and DC-coupled storage.

57

Fault codes

Device types covered

Inverter (57)

Common fault codes

Check the AC isolator and consumer unit — confirm grid is present with a voltage…

Grid Voltage Out of Range

Measure the AC voltage at inverter terminals with a multimeter. Compare to G98 l…

Grid Frequency Out of Range

Check frequency reading in Fox ESS app or on inverter display. Log frequency ove…

10-Minute Average Voltage Fault

Check 10-minute average voltage in the app. If consistently above 253 V, check e…

Inverter Overload

Check total connected AC load against inverter rated output. Identify any large …

Isolation Fault (ISO Fault)

Disconnect all strings and test each string in turn with an insulation resistanc…

All FoxESS fault codes

Check the AC isolator and consumer unit — confirm grid is present with a voltage…

Grid Voltage Out of Range

Measure the AC voltage at inverter terminals with a multimeter. Compare to G98 l…

Grid Frequency Out of Range

Check frequency reading in Fox ESS app or on inverter display. Log frequency ove…

10-Minute Average Voltage Fault

Check 10-minute average voltage in the app. If consistently above 253 V, check e…

Inverter Overload

Check total connected AC load against inverter rated output. Identify any large …

Isolation Fault (ISO Fault)

Disconnect all strings and test each string in turn with an insulation resistanc…

DC Injection Fault

Power cycle the inverter. Allow a full self-test cycle

Ground / Earth Fault

Check the PE (earth) terminal is secure at the inverter AC output. Confirm AC is…

Residual Current Fault

Check all DC connectors for moisture or damage. Inspect cable runs for pinch poi…

PV Voltage Fault

Measure open-circuit voltage of each string before connecting. Compare to invert…

PvCon Dir Fault

PV Connector Polarity Fault

Power down DC isolator. Measure polarity of each string with a multimeter at the…

BMS Lost / BMS Communication Error

Check BMS communication cable is firmly seated at both the battery and inverter …

BMS Internal Fault

Check battery status in Fox ESS app. Note any specific BMS sub-codes shown

Battery Voltage Fault

Check battery SoC and voltage in the app. If SoC is at 0%, allow trickle charge …

Battery Power Low

This is a warning state — grid will recharge battery. Review minimum SoC setting…

Bat Relay Fault

Battery Relay Open/Short

Power cycle the battery. Check all cable connections

Temperature Fault

Check ambient temperature at the installation location. Ensure ventilation clear…

Meter Lost / Meter Communication Error

Check CT clamp is securely fitted on the correct conductor (usually grid import …

SCI Fault / Internal Communication Error

Power cycle the inverter (AC off, DC off, wait 5 minutes). Check if fault clears…

Eps Relay Fault

EPS Relay Fault

Check EPS output wiring is connected to inverter EPS terminals (not AC output). …

Calculate total load on EPS circuit. Reduce non-essential loads. Check EPS rated…

Inverter / ARM EEPROM Fault

Power cycle the inverter. Check if fault clears

Arc Fault Circuit Interruption

Inspect all DC connectors for burn marks, carbonisation, or damage. Check DC ter…

SW Bus Vol Fault

DC Bus Voltage Out of Range (Software)

Power cycle (AC off, DC off, wait 5 min, restore). Confirm DC input is within MP…

HW Bus Vol Fault

DC Bus Voltage Out of Range (Hardware)

Full power cycle: AC breaker OFF, DC isolator OFF, wait 10 min, restore. Check f…

BmsCellImbalance

Battery Cell Voltage Imbalance

Balance charge: force battery to 100% SoC and hold for 2-3 hours. BMS balancing …

DSP Internal Communication Fault

Power cycle inverter. Check firmware in Fox Cloud -- all boards should be on the…

ECS: Under Voltage

Pack Under-Voltage Fault

Check SoC on Fox Cloud. If at 0% and battery has not charged for >7 days, deep d…

ECS: Over Voltage

Pack Over-Voltage Fault

Check inverter battery charge voltage setting in Fox Cloud matches the ECS batte…

Cell Over-Temperature Fault

Check ambient temperature at battery location. ECS operating range: 0–55°C disch…

ECS: PCS Comm Fail

BMS / PCS Communication Lost

Check CAN/RS485 cable is fully seated at the CM (controller module) bottom port …

ECS: Module Addr Fail

Module Addressing Failed

Count physical CS modules in the stack. Check DIP switch on CM matches. Inspect …

ECS: Relay Adhesion

Main Relay Stuck Closed (Welded)

Power off completely: DC switch off → hold POWER button for 5 seconds → wait 5 m…

ECS: Relay Not Close

Main Relay Failed to Close

Ensure inverter is powered up before pressing POWER button on battery. Correct s…

ECS: AFE Comm Fail

AFE Communication Failed

Power cycle the battery. Check if fault clears after restart

Cell 0V Fault — Dead Cell or Broken Sense Wire

Do not attempt to charge. Check if the battery has been subject to deep discharg…

Battery State of Health Low

This is not a recoverable fault — the battery has completed its usable cycle lif…

EP: PCS Comm Fail

BMS / PCS Communication Lost

Check CAN cable at EP battery COM port and inverter BMS port. On parallel EP sys…

EP: Parallel Addr Fail

Parallel Addressing Failure

Check LINK OUT of Main unit connects to LINK IN of first Slave, and LINK OUT of …

EP: Relay Adhesion

Relay Stuck Closed

Power off: POWER switch off, wait 5 minutes. Power on. Check if fault clears

EP: Deep Discharge

Battery Deeply Discharged — Recovery Required

Connect to a charge source immediately. Force-charge via inverter if needed. Che…

EP: Black Start

Black Start Mode (EPS without grid)

To activate Black Start: press POWER button 3 times within 4 seconds. EPS output…

Isolation Resistance Fault

Disconnect all PV strings and battery. Test IR of each independently at 500V DC.…

AIO: Bms Volt Low

Battery Voltage Low (AIO BMS Report)

Check SOC in Fox Cloud. If at minimum reserve, allow charge cycle to complete. C…

AIO: BmsCellImbalance

Battery Cell Voltage Imbalance

Allow the battery to complete a full charge/discharge cycle — this allows passiv…

AIO: Meter Lost

Meter / CT Communication Lost

Check CT clamp cable is plugged into the correct Meter/CT port on the AIO unit. …

AIO: EPS Over Load

EPS Output Overload

Identify and disconnect non-essential loads from the EPS circuit. Check the AIO …

Electronic Lock Fault

Remove EV plug completely. Re-insert firmly until it clicks. Retry charging. Che…

Emergency Stop Fault

Locate the E-stop button on the side of the charger. If pressed, rotate clockwis…

Output Overcurrent

Check maximum current setting in FoxSwitch app matches the installed cable ratin…

Electric Leakage / RCD Trip

Disconnect the EV. Check if fault clears when EV is disconnected. If it does, th…

L/N Reversal — Live and Neutral Swapped

Power off at MCB. Check wiring at charger terminal block — L=Brown/Black, N=Blue…

Charging Interface Overtemperature

Power off charger. Inspect socket contacts for burn marks, discolouration, or ar…

CT Clamp Reversed — Solar Divert Not Working

Check CT clamp arrow: must point toward the charger (away from grid/supply). Rev…

Dongle Not Connected to Router

Connect phone/laptop to dongle's own hotspot (SSID: W-xxxxxxx, default password:…

Router Connected But Cloud Unreachable

Confirm broadband is working (test on another device). Port 443 must be open to …

Dongle Not Powered / Not Recognised

Unscrew and remove the dongle. Re-insert fully — triangle logo must face front o…

Full decision tree available in Faultpath Pro

Step-by-step fault diagnosis, offline access, and complete fault code coverage for solar & battery engineers.

Get Faultpath Pro