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Fault code index · Fox ESS inverters & batteries

Fox ESS Fault Code Index

What Fox ESS inverter and battery alarms mean, taken from Fox's own manuals, and what Fox says to do about each one. Find yours by name, or by the number Fox Cloud shows beside it.
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  • Names and actions from Fox ESS's H1(G2)/AC1(G2) and H3-Plus/P3-Plus manuals
  • All Fox ESS models
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Ron is incredibly knowledgeable about solar installs in general but knows givenergy products inside out and the key personnel that worked there from the start to the end. My problem was spurious in its nature but Ron spotted it straight away when he understood the installation details. In essence the installers didn’t fit the correct trip switch. He also gave me hope that in the future hardware repairs could be possible but it’s still early days. This guy really is in the know and keen to sucas a business If you need help don’t hesitate

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Massively massively recommended. We had a big battery array (49kW across three phases) put in four years ago. c £35k cost. It’s been a total nightmare for many reasons, not least 1. our installer being totally useless and unresponsive and 2. Givenergy, our battery supplier, going bust. Long story short it had never worked anywhere near properly despite countless hours on phones and emails; the best we’d achieved was one third of the batteries working. Rather than write it off, I asked a PM friend to try to source someone who could come on site and review and revive the system. He found Solar Tech Support and Ron. Ron assured us he was the man to get it going again. After so many years of pain, I was not convinced but, true to his word, five hours later it was up and running. Lovely chap, super knowledgeable with a support team to lean on who are also clearly super technical. I honestly didn’t think there was much chance of getting this array going ever again so was absolutely delighted when Ron and team pulled it off. Bravo!

Will Wynne · Jun 2026 Google

Ron diagnosed the problem remotely - efficiently and order the part identified as the fault - this part came directly from to me and Ron visited within a few days and within the hour corrected the problem and since everything has been excellent -highly recommended - very pleasant manner and lovely to work with . Ivor Morris.

Ivor Morris · Jul 2026 Google

Ronald was able to organise a brilliant electrician with extensive experience of GivEnergy systems local to me in the SW. I have now got a fully functioning system and suspect that my electricity bill will be substantially reduced or in credit over a year. Also when said electrician discovered an overvoltage in the my local grid, Ronald prepared a very lucid and comprehensive report of the situation which I have now supplied to my local grid. Cannot recommend Ron and Dan enough.

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Fox ESS alarm names and numbers

Fox ESS's manuals for the H1(G2)/AC1(G2), first-generation H1/AC1, KH/KA and H3/AC3 give each alarm a name, such as Grid Volt Fault or BMS Lost, and print no numbers. Fox Cloud prints a number beside each alarm in its alarm export, and its wording can differ from the manual's name. Fox's manual for the commercial H3-Plus/P3-Plus gives every alarm a four-digit code, such as 1145, and the EVO 10 manual shows battery faults as codes such as BS1 E04.

So each row below leads with Fox's alarm name and Fox's action, with any number beside it. We cover all Fox ESS models. The H1(G2), AC1(G2), first-generation H1/AC1, KH/KA and H3/AC3 share most of these names, and the AC1 and AC3 have no solar input.

Fox writes its manuals for qualified electricians, so where Fox's action is a check of cables, wiring or connections, it's a job for your installer or an engineer, not for you. Where Fox says to contact Fox ESS, Fox ESS UK tells owners to contact their installer first, and its warranty claims are made by the installer. If your Fox ESS installer has gone bust, we can be the Local Installer you appoint to make the claim. How we make a Fox ESS claim.

NumberFox's alarmWhat the number's source says
1Grid Lost FaultNo Utility
14BMS LostBMS communication
25Over Current Protect FaultOver Current Protect Fault, on a KH-series export
26Grid Volt FaultGrid Voltage Fault
27Grid Freq FaultGrid Frequency Fault
2810min Volt Fault10 Minute Average Grid Voltage Fault
194Bms Volt HighBattery over voltage
195Bms ChgCur HighCharging over current
222Bms ChgReq NoAckBMS charge request, no reply
234No Fox alarm nameFox publishes no meaning
240No Fox alarm nameCT or meter not detected
242Meter Lost FaultMeter lost
1145, 1181, 1294Arc Fault, Arc Permanent Fault, AFCI fault lock deviceH3-Plus/P3-Plus manual
40004 and other five-digit numbersApp messages, not in the manuals' alarm listsSee the last group

marks the alarms we'd always hand to an engineer: don't keep clearing them. Where a row says a full restart, this is what we mean. Our order for a Fox ESS system is the battery's power button first, then the AC isolator, then the inverter's DC isolator, and the battery's DC MCB last if it has one, so the MCB is never switched under load. To turn it back on, go in reverse: battery DC MCB, DC isolator, AC isolator, then the battery's power button. Read the full shutdown guide.

Grid & AC faults

Alarms about the mains supply: the grid lost, or its voltage or frequency out of range. Fox's manual says the system reconnects by itself once the grid is back to normal, and to contact Fox ESS if it doesn't.

Grid Lost FaultGrid supply lost · Fox Cloud code 1
Fox says the grid is lost. Fox's action: the system reconnects by itself when the grid is back to normal, and to contact Fox ESS if it doesn't. Fox Cloud's export shows it as code 1, "No Utility". Owners report this alarm in power cuts, often with Grid Volt Fault and Grid Freq Fault. Fox ESS grid fault guide →
Grid Volt FaultGrid voltage out of range · Fox Cloud code 26
Fox says grid voltage is out of range. Fox's action: the system reconnects by itself when the grid is back to normal, and to contact Fox ESS if it doesn't. The UK supply should stay between 216 V and 253 V, the legal limits. The inverter's own protection settings are wider and are set at commissioning: in Great Britain, G98 and G99 give 184 V on the low side and 262.2 V and 273.7 V on the high side, each with its own delay. Fox's Tech Hub says the inverter raises its output voltage to export, and on a weak grid that can cause trips, so a fault in daylight hours only may be the inverter's own export. An export limit is an installer setting, and protection settings can only be changed with the network operator's written agreement. If the voltage is consistently above 253 V, that may be a supply issue for your network operator. Fox ESS grid fault guide → Field note: proving grid over-voltage to the network operator →
Grid Freq FaultGrid frequency out of range · Fox Cloud code 27
Fox says grid frequency is out of range. Fox's action: the system reconnects by itself when the grid is back to normal, and to contact Fox ESS if it doesn't. In Great Britain, G98 and G99 set the settings: the inverter stays connected inside the band for the periods the standard allows, and trips at 47.5 Hz after 20 s, 47.0 Hz after 0.5 s and 52.0 Hz after 0.5 s. 49.5 to 50.5 Hz is the statutory band the network must hold, not an inverter setting. These settings can only be changed with the network operator's written agreement. Fox ESS grid fault guide →
10min Volt FaultVoltage out of range over 10 minutes · Fox Cloud code 28
Fox says the grid voltage has been out of range over the last 10 minutes. Fox's action: the system reconnects by itself when the grid is back to normal, and to contact Fox ESS if it doesn't. Fox Cloud's export calls it "10 Minute Average Grid Voltage Fault", and on the H3 Smart, Fox's release notes call it a 10-minute overvoltage fault. If it appears repeatedly during peak solar hours, tell your installer: an export limit is an installer setting and may reduce the inverter's contribution to local voltage rise. Fox ESS grid fault guide → Field note: proving grid over-voltage to the network operator →
Over Load FaultOverload in on-grid mode
Fox says there's an overload in on-grid mode. Fox's action: check whether the load exceeds the limit, or contact Fox ESS. Reduce what the house is using and see if it clears.

Ground & safety faults

Alarms about insulation, residual current and the earth connection. Iso Fault is insulation on the solar side, Ground Fault is the earth connection, and Bms Insul Fault, in the battery group, is the battery's own insulation. Fox gives their checks to qualified electricians.

Iso Fault Insulation check failed on the solar side
Fox says the isolation (insulation) check has failed. This is the solar (PV) side. Fox's action: check whether the insulation of the cables is damaged, see whether it returns to normal, or contact Fox ESS. Damp or damaged insulation on the solar side can cause it, and checking cable insulation is an electrician's job. Don't keep clearing it: call an engineer. Fox ESS ground fault and Iso Fault guide →
DCI Fault DC in the output current over the limit
Fox says the DC component in the output current is over the limit. Fox's action is to disconnect PV, grid and battery, then reconnect, which is an electrician's job, and to contact Fox ESS if it doesn't return to normal. Don't keep clearing it: call an engineer.
Ground Fault Earth connection failed
Fox says the ground (earth) connection has failed. Fox's action is to check the voltage between neutral and earth, check the AC wiring, then disconnect PV, grid and battery and reconnect. Those are an electrician's checks. If it persists, the AC installation may have an earth fault, which needs an electrician to find. Don't keep clearing it: call an engineer. Fox ESS ground fault and Iso Fault guide →
Res Cur Fault Residual current high
Fox says the residual current is high. Fox's action: check whether the cable insulation is damaged, see whether it returns to normal, or contact Fox ESS. Fox says residual current can come from damaged insulation, or from normal leakage that rain and humidity affect. Checking cable insulation is an electrician's job. Don't keep clearing it: call an engineer. Fox ESS ground fault and Iso Fault guide →
Res Cur HW Fault Residual current detection device failed
Fox says the residual current detection device has failed. Fox's action is to disconnect PV, grid and battery, then reconnect, which is an electrician's job, and to contact Fox ESS if it doesn't return to normal. Don't keep clearing it: call an engineer. Fox ESS ground fault and Iso Fault guide →

Solar & PV faults

Alarms about the solar (PV) inputs: their voltage, their current and their polarity. The AC1 and AC3 are AC-coupled and have no solar input, so these rows don't apply to them.

Pv Volt FaultPV voltage out of range
Fox says PV voltage is out of range. Fox's action: check the output voltage of the PV panels, or contact Fox ESS. Measuring panel voltage is an electrician's job.
SW Pv Cur FaultPV input current high (software)
Software has detected high PV input current. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal. Whether the solar array suits the inverter's input limits is for the installer to check.
HW Pv Cur FaultPV input current high (hardware)
Hardware has detected high PV input current. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal. On the H3/AC3, Fox says to check the PV positive and negative are properly connected, which is an installer's check. If it keeps coming back, it needs a qualified engineer.
PvCon Dir Fault PV connection reversed
Fox says the PV connection is reversed. Fox's action: check the PV positive and negative are connected the right way round, or contact Fox ESS. Fox's manuals say a DC connector may be separated only when no current is flowing on it, so this is an installer's job, never an owner's. Don't keep clearing it: call an engineer.

Battery & BMS faults

Alarms about the battery, its management system (BMS) and its link to the inverter. The Bms alarms name no battery model, so they apply to whichever Fox battery is fitted, such as an EP, EQ or ECS. For 20 of them, from Bms Volt High to Bms ChgReq NoAck, Fox's only action is to contact the battery supplier, or Fox's service department on the KH/KA. Fox's newest H1(G2) manual spells these "BMS …", for example BMS Volt High and BMS CellImbalance, so look for either spelling. Each battery also has its own lights: see the last row.

BMS LostBattery link interrupted · Fox Cloud code 14
Fox says communication between the BMS and the inverter is interrupted. Fox's action: check the communication cable between the battery and the inverter is correctly and securely connected, which is your installer's job. Fox ESS BMS communication guide →
Bms Ext FaultBattery link interrupted
Fox gives this the same words as BMS Lost: communication between the BMS and the inverter is interrupted. Fox's action: check the communication cable between the battery and the inverter, which is your installer's job. Fox ESS BMS communication guide →
Bms Int FaultDIP switch or link between battery packs
Fox says a DIP switch is in the wrong position, or communication between the battery packs is interrupted. Fox's action: set the DIP switch to the correct position and check the cable between the packs. Both are your installer's checks. Fox ESS BMS communication guide →
Bms Volt HighBattery over-voltage · Fox Cloud code 194
Fox says battery over-voltage. Fox's action: contact the battery supplier. Owners report a battery firmware update ending repeats of this alarm, and a moderator on Fox's Tech Hub forum told one owner it could be down to firmware. Don't open the battery case or disconnect its cables: Fox lets only qualified technicians with its approval open a battery. Fox ESS battery manuals →
Bms Volt LowBattery under-voltage
Fox says battery under-voltage. Fox's action: contact the battery supplier. Check the state of charge in the FoxCloud 2.0 app. Min SOC settings are normally set at commissioning, so ask your installer before changing one. Fox's battery manuals say an over-discharged battery should be recharged within seven days, and only a qualified technician with Fox's written approval may recharge a deeply discharged one. Don't force-charge it or keep switching it off and on to wake it. Fox ESS battery not charging guide →
Bms ChgCur HighBattery charging current too high · Fox Cloud code 195
Fox says battery charge over-current. Fox's action: contact the battery supplier. Fox Cloud's alarm table gives 195 as charging over current, though one owner reported it as a battery voltage fault. Fox ESS battery manuals →
Bms DchgCur HighBattery discharge current too high
Fox says battery discharge over-current. Fox's action: contact the battery supplier. Fox ESS battery manuals →
Bms Temp HighBattery too hot
Fox says battery over-temperature. Fox's action: contact the battery supplier. Fox ESS battery manuals →
Bms Temp LowBattery under-temperature
Fox says battery under-temperature. Fox's action: contact the battery supplier. Fox's Tech Hub says batteries without internal heating charge only between 0 °C and 55 °C and go dormant outside that range until it returns, but that isn't a rule for every Fox battery: the EVO 10 manual says its batteries charge above -20 °C or -10 °C, depending on the cell type, even with heating off. The ECS has no heater and charges from 0 °C, Fox ESS UK says the EQ4800 has no warm-up, and warming is off when EQ batteries are mixed with ECS. The EP range is the main one in the UK with a heater: with warm-up on, Fox's July 2026 datasheets rate the EP5 and EP6 to charge from -25 °C. Where a battery has warm-up, its settings are in the FoxCloud 2.0 app. Insulating the space round a battery, or moving it, is your installer's decision, and no insulating material may touch the battery. A faulty temperature sensor has its own alarm, BmsTempSen Fault. Fox ESS battery not charging guide →
BmsCellImbalanceCell capacities differ
Fox says the capacities of the cells are different. Fox's action: contact the battery supplier. Don't open the battery or try to balance its cells: Fox's battery manuals leave repairs to Fox. Fox ESS battery manuals →
Bms HW ProtectBattery hardware protection active
Fox says the battery's hardware is under protection. Fox's action: contact the battery supplier. Fox ESS battery manuals →
BmsCircuit FaultBMS circuit fault
Fox says BMS hardware circuit fault. Fox's action: contact the battery supplier. Fox ESS battery manuals →
Bms Insul Fault Battery insulation fault
Fox says battery insulation fault. Fox's action: contact the battery supplier. Fox lists it with the battery alarms, separately from the inverter's Iso Fault on the solar side. Don't keep clearing it: call an engineer. Fox ESS battery manuals →
BmsVoltsSen FaultBattery voltage sensor fault
Fox says battery voltage sensor fault. Fox's action: contact the battery supplier. Fox ESS battery manuals →
BmsTempSen FaultBattery temperature sensor fault
Fox says battery temperature sensor fault. Fox's action: contact the battery supplier. Fox ESS battery manuals →
BmsCurSen FaultBattery current sensor fault
Fox says battery current sensor fault. Fox's action: contact the battery supplier. Fox ESS battery manuals →
Bms Relay FaultBattery relay fault
Fox says battery relay fault. Fox's action: contact the battery supplier. Fox ESS battery manuals →
Bms Type UnmatchBattery packs of different capacity
Fox says the battery packs have different capacities. Fox's action: contact the battery supplier. Fox ESS BMS communication guide →
Bms Ver UnmatchSlave packs on different software
Fox says the software differs between the slave packs. Fox's action: contact the battery supplier. Fox ESS BMS communication guide →
Bms Mfg UnmatchCells from different makers
Fox says the cell manufacturer is different. Fox's action: contact the battery supplier. Fox ESS BMS communication guide →
Bms SwHw UnmatchSlave software and hardware don't match
Fox says a slave pack's software and hardware don't match. Fox's action: contact the battery supplier. Fox ESS BMS communication guide →
Bms M&S UnmatchMaster and slave software don't match
Fox says the master's and slaves' software don't match. Fox's action: contact the battery supplier. Fox ESS BMS communication guide →
Bms ChgReq NoAckNo response to a charging request · Fox Cloud code 222
Fox says there was no response to a charging request. Fox's action: contact the battery supplier. Fox ESS BMS communication guide →
Code 234Reported with battery faults · no meaning published
Owners report code 234 with battery faults, and Fox publishes no meaning for it. A moderator on Fox's Tech Hub forum told one owner it could be down to firmware. Note any alarm name shown with it and when it started.
Bat Volt FaultBattery voltage fault
Fox says battery voltage fault. Fox's action: check the battery input voltage is within the normal range, or contact Fox ESS. Measuring battery voltage isn't an owner job, and the normal range for each Fox battery is on its datasheet. If the app shows Bms Volt High or Bms Volt Low instead, see those rows: Fox gives them a different action. Fox ESS battery datasheets →
SW Bat Cur FaultBattery current high (software)
Software has detected high battery current. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal.
HW Bat Cur FaultBattery current high (hardware)
Hardware has detected high battery current. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal.
Bat Power LowBattery charge low
Fox says the battery power is low. Fox's action: let the battery recharge, or contact Fox ESS. We'd also check in the app that charging is enabled and your schedule is set as you intended. Fox ESS battery not charging guide →
BatCon Dir Fault Battery connection reversed
Fox says the battery connection is reversed. Fox's action: check the battery positive and negative are connected the right way round, or contact Fox ESS. That check is at the battery's terminals, so it's an installer's job. Don't keep clearing it: call an engineer.
Bat Relay OpenBattery relay stays open
Fox says the battery relay stays open. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal.
Bat Relay Short CircuitBattery relay stays closed
Fox says the battery relay stays closed. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal.
Bat Buck Fault / Bat Boost FaultBattery buck or boost circuit failed
Fox says a part in the battery's buck or boost circuit has failed. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal. On the H3/AC3, Bat Boost Fault can also mean the relay on the battery side hasn't closed, and Fox advises master firmware 1.69 or later. Firmware update risks →
Battery lightsFaults shown on the battery itself
Fox's ECS, EQ and EP5 battery manuals show faults as light patterns on the battery, not as codes, for faults such as under-voltage, over-temperature and relay adhesion. Fox says a flashing light may only be an alarm or a protection, which normally needs no action and clears once its cause has gone. If the alarm shows on both the battery and the inverter, Fox says to contact the local distributor. On the ECS, standby shows as the green light flashing with the red light off. Fox ESS battery manuals →

DC bus & inverter hardware

Alarms inside the inverter: its DC bus voltage, output current, temperature, memory and sampling circuits. "SW" means software has detected the fault and "HW" means hardware has, and Fox gives both the same action.

SW Bus Vol FaultBus voltage out of range (software)
Software has detected the bus voltage out of range. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal. On the H3/AC3, Fox also says to check the neutral on the grid port, an installer's check, and advises master firmware 1.69 or later. Fox ESS UK says anyone can ask for an inverter firmware update by emailing its service team with the inverter's serial number. Firmware update risks →
HW Bus Vol FaultBus voltage out of range (hardware)
Hardware has detected the bus voltage out of range. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal.
SW Inv Cur Fault / HW Inv Cur FaultOutput current high (software or hardware)
Software or hardware has detected high output current. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal. For SW Inv Cur Fault on the H3/AC3, Fox advises master firmware 1.69 or later. Firmware update risks →
Over Current Protect FaultOver-current protection · Fox Cloud code 25
Fox Cloud's export shows this as code 25 on a KH-series inverter. It isn't in the H1(G2) manual's alarm list, so there's no Fox action to quote here. If it keeps coming back, it needs a diagnosis.
Temp FaultInverter temperature high
Fox says the inverter temperature is high. Fox's action: check the temperature where the inverter is, see whether it clears, or contact Fox ESS. Fox asks for 300 mm of clear space round the H1(G2), the first-generation H1 and the KH, and Fox ESS UK's current H3/AC3 manual asks for 300 mm at the sides and 500 mm above and below. An enclosure mustn't be airtight. Fox ESS UK lets an installer depart from these clearances where airflow and access are kept, and Fox advises avoiding long spells of direct sun where possible. If it looks tight, ask your installer rather than moving anything. Many Fox inverters are rated to run up to 60 °C and start to reduce output from 45 °C, and your model's datasheet gives its range.
Inv EEPROM Fault / ARM EEPROM FaultMemory fault (inverter or manager)
Fox says there's a fault in the inverter's or the manager's EEPROM, its memory. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal. Firmware updates by USB aren't part of Fox's action here. They need a U-disk under 32 GB, formatted FAT16 or FAT32, USB 2.0 only, with the files from Fox ESS support, and the waterproof lid has to be unscrewed, so that's an installer's job.
MDSP Smpl Fault / RDSP Smpl FaultSampling circuit failed (master or slave)
Fox says the master's or the slave's sampling and detection circuit has failed. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal.

Relay & EPS faults

Alarms about the inverter's grid relays and its EPS (backup) output. For the relay alarms, Fox's action is a full restart, then Fox ESS if the alarm stays.

Main Relay OpenGrid relay stays open
Fox says the grid relay stays open. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal. The H3/AC3 manual doesn't list this alarm.
S1 / S2 / M1 / M2 Close FaultGrid relay stays closed
Fox says grid relay S1, S2, M1 or M2 stays closed. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal.
Eps Relay FaultEPS relay failed
Fox says the EPS relay has failed. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal. Fox ESS EPS not working guide →
Eps Over LoadOverload on the EPS (backup) output
Fox says there's an overload in off-grid (EPS) mode. Fox's action: check whether the EPS load exceeds the limit, or contact Fox ESS. During a power cut, the inverter can only supply a limited amount of power to backed-up circuits. Fox gives the maximum by model: up to 6.0 kVA on the H1(G2) range, with a higher figure for 60 seconds, and 5 to 12 kVA on the three-phase H3/AC3, of which at most a third is available on any one phase when off-grid. Fox advises against inductive loads on the EPS output, and our advice is no kettles, ovens or immersion heaters. Fox ESS EPS not working guide →

Communication & internal faults

Alarms about the links inside the inverter, between its master, slave and manager controllers, and about the link to the external meter. For the internal links, Fox's action is a full restart, then Fox ESS. Meter Lost Fault is the cable to the meter, which your installer checks: see Meter Lost Fault and CT not detected.

Meter Lost FaultMeter link lost · Fox Cloud code 242
Fox says communication between the meter and the inverter is interrupted. Fox's action: check the cable between the meter and the inverter is correctly and securely connected, which is your installer's job. An installer also checks 9600 baud, address 1 on Fox's DTSU666 meter. On the H1(G2) with an export hard limit set, losing the CT or meter link makes the inverter disconnect from the grid and shut down. Meter Lost Fault and CT not detected guide →
Code 240CT or meter not detected
Code 240 means the CT or meter isn't detected, and a firmware mismatch after a battery change can cause it too. Owners report it with the words "fail to detect CT". Fox says a hybrid with no batteries and no CT must have its CT option switched off, or the inverter goes into an error state, and its single-phase CT guidance says a CT is compulsory on any installation with batteries. Owners also report the Meter/CT setting changing after a firmware update. Checking the CT's direction and cable, and the meter's wiring and address, is your installer's job. On Fox's commercial H3-Plus/P3-Plus, code 1292 "Meter's CT line fault" means check the meter's CT cables, and Fox doesn't say it's the same as 240. Meter Lost Fault and CT not detected guide → Field note: a Fox ESS code 240 case →
SCI FaultMaster-to-manager link failed
Fox says communication between the master and the manager has failed. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal. One owner reports it clearing after a firmware update from a USB stick Fox sent, and a USB update is an installer's job. Fox ESS UK says anyone can ask for an inverter firmware update by emailing its service team with the inverter's serial number. Firmware update risks →
MDSP SPI Fault / RDSP SPI FaultMaster-to-slave link failed
Fox says communication between the master and the slave has failed. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal.
GridV / GridF / Dci / Rc Cons FaultMaster and slave readings don't agree
Fox says the master's and the slave's readings of grid voltage, grid frequency, DCI or residual current don't agree. Fox's action: a full restart, then contact Fox ESS if it doesn't return to normal.

Arc & AFCI faults (H3-Plus/P3-Plus codes)

Four-digit codes from Fox ESS's manual for the H3-Plus/P3-Plus, a commercial three-phase range of 50 to 125 kW, read in issue V1.2 and unchanged in issue V1.4 EU. The AFCI, Fox's arc-fault protection, is standard on the H3-Plus/P3-Plus and optional on the H1(G2), whose manual lists no arc alarm.

Arc Fault / Arc Permanent Fault / AFCI fault lock device DC arc detected · codes 1145, 1181, 1294 (H3-Plus/P3-Plus)
Fox says the AFCI has detected a DC arc between the solar panels and the inverter and has stopped the inverter, and that arcs can lead to fires. Fox names poorly connected or damaged panels and cables, and DC connectors that aren't firmly in place, as causes. Fox's action for 1145 is to find and fix the poor contact before the alarm is cleared and the inverter restarted. Fox says alarms 1 to 4 in a day clear after 5 minutes, and 5 or more in 24 hours lock the unit until it's cleared by hand, at its web server or in Fox Cloud's Remote Setting, or until the next day. For 1181, Fox's action is a check of the PV cables, a set switch-off and restart, then the installer. Finding and fixing the contact is an engineer's job, because solar panels and their cables are live in daylight. Don't keep clearing it: call an engineer.

Fox Cloud app & account messages

Owners report these numbers in the Fox Cloud app, and two are in Fox's Open API document. None is in the alarm lists of the Fox inverter manuals we've read.

40004Fox Cloud app message · one owner's report
No Fox ESS document explains 40004. One owner on FoxESS Community, an independent forum, reported it at the app's sign-in in June 2026 on app version V2.2.16, with foxesscloud.com and the inverter working normally, and changing the app's region and language to Europe and English let them in, though that's a workaround and not a fix from Fox. What one owner reported about 40004 →
41201Fox Cloud app message · owners' reports
Owners report it as a "server exception" that stopped a setting being saved.
41206Fox Cloud app message · owners' reports
Owners report it after a datalogger firmware update failed.
44098Fox Cloud app message · owners' reports
Owners report it when a change to Max SOC failed to save in FoxCloud 2.0.
40256Open API message · Fox's Open API document
Fox's Open API document says the request's required headers are missing or wrong. It concerns people who connect other apps to Fox's Open API.
40400Open API message · Fox's Open API document
Fox's Open API document says too many requests were made.
Alarm or number not listed here?

Fox's alarm lists differ by model range: the H1(G2), first-generation H1, KH/KA and H3/AC3 manuals name their alarms, and the commercial H3-Plus/P3-Plus manual gives every alarm a four-digit code. Send us the alarm text exactly as the display or the FoxCloud 2.0 app shows it, with any number and your model, and we'll look it up. If you have no alarm at all, start from the symptom on our Fox ESS problems page. For other owners' experience, FoxESS Community (foxesscommunity.com) is an independent owners' and installers' forum, and Fox ESS UK runs its own forum on its Tech Hub (fox-ess.tech/community/), where Fox staff reply. Numbers such as 40004 are app messages: see the last group above.

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Fox ESS guides by fault type
BMS communication fault

BMS Lost · Bms Int · 14 · 222What BMS Lost means, and how a battery that drops offline is diagnosed.

See BMS communication fault
Grid voltage & frequency fault

Grid Lost · Grid Volt · Grid Freq · 10min VoltFox's four grid alarms, and what to do about a high supply voltage.

See grid voltage & frequency fault
Battery not charging

Work mode · charge scheduleWork modes and charge schedules when a Fox battery won't charge.

See battery not charging
EPS not working

Eps Over Load · Eps Relay · EPS offWhy Fox ESS backup (EPS) doesn't start in a power cut.

See EPS not working
Ground fault & isolation fault

Iso Fault · Ground Fault · Res Cur Fault · Res Cur HW FaultGround Fault and Iso Fault: two different alarms, and what each one means.

See ground fault & isolation fault
Meter Lost Fault & CT not detected

Meter Lost · CT not detected · 240 · 242What Fox's meter and CT alarms mean, what you can check in the app, and when it's an installer's job.

See Meter Lost Fault & CT not detected
Fox Cloud offline

Offline · WiFi dongle · 40004When the FoxCloud 2.0 app shows your system offline, and how a WiFi dongle is reconnected.

See Fox Cloud offline
Explore

More Fox ESS help

Fox ESS hub

Help with Fox ESS inverters and batteries in the UK: fault codes, Fox Cloud offline, EPS backup and battery alarms. Not affiliated with or endorsed by Fox ESS.

See Fox ESS hub
Fox ESS problems

Fox ESS fault guides: battery not charging, BMS comms, grid faults, EPS backup, ground fault and Fox Cloud offline. Not affiliated with or endorsed by Fox ESS.

See Fox ESS problems
Fox ESS documents

Download Fox ESS datasheets and manuals for the H1 (G2), H3, EVO and the EP, EQ and ECS batteries, plus quick installation guides for the H3 and H3 Smart.

See Fox ESS documents
How to read inverter fault codes

Learn how to find and read solar inverter fault codes across all major UK brands including GivEnergy, Growatt, Sunsynk, SolarEdge, Solis, Huawei, Fox ESS.

See how to read inverter fault codes
Firmware update risks

Before updating inverter or battery firmware, know the risks: settings resets, stalled updates, version clashes and bricked hardware, and how to recover.

See firmware update risks
Find your inverter

Not sure which solar inverter brand you have? Identify it from the label, the monitoring app, or the MCS certificate, with notes on every major UK brand.

Find your inverter
FAQ

Fox ESS fault code questions

In the FoxCloud 2.0 app, alarms sit under the bell icon at the top right, in Current and History lists (older versions of Fox's app manual call the screen Faults, under Me). The Fox Cloud web portal is at foxesscloud.com. On the H1(G2), AC1(G2), first-generation H1/AC1 and KH/KA, the inverter's own menu has History, then Error log, which lists past alarms, and on the H1(G2) and KH/KA a red light on the panel means it's in fault mode. Note the alarm name exactly as shown, any number beside it and when it started, before anything else is done.
Grid alarms clear by themselves once the supply is back to normal, and many others clear after a full restart: the whole system off and back on in order, not one device. One that keeps coming back needs a diagnosis, and an alarm marked needs an engineer rather than another restart. Our shutdown guide gives the order for a Fox ESS system.
In Fox's alarm list, the 20 alarms from Bms Volt High to Bms ChgReq NoAck all have one action: contact the battery supplier, or Fox's service department on the KH/KA. BMS Lost, Bms Ext Fault and Bms Int Fault are about the link from the battery to the inverter or between battery packs, and Fox's action is a check of that cable or of a DIP switch, which is your installer's job. The "Bat" alarms have other actions: for Bat Volt Fault, check the battery input voltage is within its normal range, and for Bat Power Low, let the battery recharge. Measuring a battery's voltage isn't an owner job.
Our remote diagnostic is free. If the fault can be fixed remotely after all, it's £125, and only if we fix it. A hardware repair on site is from £295, quoted in writing before we start. If the inverter or battery is under Fox's warranty, Fox ESS UK's policies say your installer makes the claim, but if your Fox ESS installer has gone bust, we can be the Local Installer you appoint to make the claim, at £125 per case, plus any charge Fox makes if a unit sent back to it shows no qualifying fault.
We found no separate fault-code list from Fox ESS: the alarm list is part of each inverter's user manual, section 9.1 in the H1(G2)/AC1(G2) manual (issue V1.1.1). Our Fox ESS documents page holds copies of the H1(G2)/AC1(G2) and H3/AC3 manuals. Of the Fox manuals we've read, only the one for the commercial H3-Plus/P3-Plus gives every alarm a number, a four-digit code. For the other ranges, Fox Cloud's alarm export prints the numbers.
Usually the same day. The remote diagnostic is one session (30 min), and having the alarm name, any number, when it started and your inverter and battery models to hand makes the most of it. A screenshot of the alarm in the FoxCloud 2.0 app, under Current or History, helps too. We get access through an account transfer (£95) or you sharing your login, with your permission.
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Got an error code and need it diagnosed?

Share the exact alarm name and any number from the FoxCloud 2.0 app or the inverter's display, what the system is doing and when it started. We'll identify the cause and tell you whether it needs a remote settings fix, a site visit or a warranty claim.

  • Not affiliated with or endorsed by Fox ESS
  • No fix, no fee covers remote fixes. On-site work is quoted in writing before we start.
  • Written report with cause and recommended action

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Call 07944 877 329 Book free diagnostic