Troubleshooting · 5 min · Updated 11 October 2026

FoxESS error codes explained

Short answer: FoxESS error codes fall into four groups: the grid (for example Grid Lost Fault), the solar panels (for example Pv Volt Fault and Iso Fault), the battery (for example BMS Lost) and internal faults. Grid faults often clear by themselves when the grid is normal again. Faults that persist or return must be handled by a professional.

The tables below are based on the fault list in FoxESS' user manual for the H3/AC3 series (version 1.0.4). Other FoxESS series use many of the same names, but spelling and limits can vary. Always check the manual for your exact model if you can.

First: safety

Never open the inverter or the battery.
Do not touch DC cables from the panels. They can be live when the sun shines.
Only use the switches your installer has shown you.
Write down the error code before doing anything. FoxESS recommends this too in its troubleshooting section.

Grid faults

These faults mean the inverter has detected something outside the allowed range on the grid. It is a safety function.

Error code	Meaning according to FoxESS	What you do
Grid Lost Fault	The grid is lost	The system reconnects when the grid is normal
Grid Volt Fault	Grid voltage out of range	As above
Grid Freq Fault	Grid frequency out of range	As above
10min Volt Fault	Grid voltage too high over the last 10 minutes	As above
PLL_OverTime	Three-phase system connected to single phase	As above. If it persists, call your installer.

FoxESS' advice is the same for all five: the system reconnects by itself when conditions are normal, otherwise seek help. During a local power cut, Grid Lost Fault is expected.

If voltage faults keep returning on sunny days, it may be about local grid conditions. An electrician or your grid operator must assess that.

Solar panel (PV) faults

Error code	Meaning according to FoxESS	What you do
Pv Volt Fault	PV voltage out of range	Panel voltage must be measured by a professional
Iso Fault	The insulation test failed	Wait and see whether it clears. Call if it returns.
Res Cur Fault	High residual current	As Iso Fault
PvCon Dir Fault	PV plus and minus are swapped	Must be corrected by an installer
SW/HW Pv Cur Fault	Current from the panels too high	Restart as per the manual. Call if it returns.

According to FoxESS, Iso Fault and Res Cur Fault can be caused by damaged cable insulation. Moisture may also play a part, but a professional must assess it. These are exactly the faults you should not fiddle with yourself.

Battery faults

Error code	Meaning according to FoxESS	What you do
BMS Lost	No communication between BMS and inverter	The communication cable must be checked
Bms Ext Fault	As above	As above
Bms Int Fault	DIP switch in the wrong position, or packs not communicating	Needs an installer
Bat Volt Fault	Battery voltage out of range	Seek help
Bms Volt High / Low	Battery over or under voltage	FoxESS says: contact the battery supplier
Bat Power Low	The battery is nearly empty	Wait until it charges
BatCon Dir Fault	Battery plus and minus are swapped	Needs an installer
Eps Over Load	Overload in backup (off-grid) mode	Switch off large loads on the backup output

Bat Power Low is not really a fault. It can appear after a long period with little sun, or after a power cut where the battery supplied backup.

Internal and communication faults

Error code	Meaning according to FoxESS
Temp Fault	The inverter is too hot. Check the ambient temperature.
Ground Fault	The ground connection failed
Over Load Fault	Overload in grid-tied mode
DCI Fault	DC component in the output current above the limit
SCI Fault, MDSP/RDSP SPI Fault	Internal communication between control units fails
Inv/ARM EEPROM Fault	Memory fault in the inverter
Grid Relay Fault, Eps Relay Fault	A relay does not open or close correctly
Meter Lost Fault	No communication between the meter and the inverter

For most internal faults, FoxESS recommends disconnecting PV, grid and battery and reconnecting, and otherwise seeking help. For some faults the manual also says the software must be updated to a specific version. That requires access through FoxCloud or the installer.

Meter Lost Fault is worth knowing: the inverter may produce fine, but it cannot see your home's consumption. That can give wrong consumption and grid figures in the app.

When a fault keeps returning

Note the error code, date and time. FoxCloud also keeps an alarm history.
Note the weather. Did it happen in rain, frost or strong sun?
Check whether others nearby had a power cut.
Contact your installer with the details.

FoxESS' warranty policy for Europe says that a warranty claim is raised by the installer or authorized FoxESS staff.

If you have no installer

If your installer has closed, we can help you interpret the fault in FoxCloud with you over the phone. See packages and the FAQ.

FAQ

What does Grid Lost Fault mean on a FoxESS inverter?

The inverter has lost its connection to the grid. FoxESS writes that the system reconnects when the grid is normal. If it persists, the connection must be checked by a professional.

Is Iso Fault dangerous?

According to FoxESS, Iso Fault means the insulation test failed, for example because of damaged cable insulation. Wait and see whether it clears, and contact an electrician if it returns. Never touch DC cables from the panels.

What does BMS Lost mean?

Communication between the battery management system (BMS) and the inverter is lost. FoxESS recommends checking that the communication cable between BMS and inverter is correct and well connected.

Can I reset a FoxESS fault myself?

Many faults in FoxESS' manual carry the advice 'disconnect PV, grid and battery, and reconnect'. Only do this with the switches your installer has shown you, and in the order the manual gives. If in doubt, call first.