Ron was really helpful. He remotely adjusted my battery settings on the same day I contacted him, and at a reasonable price. Great service.
Jackie Palman · Jun 2026 Google
Diagnostic guide · Fox ESS
Fox ESS grid code fault — voltage & frequency diagnosis
H1 inverter showing error codes 26, 27, or 28? These are grid protection faults — the inverter has detected voltage or frequency outside UK limits and disconnected to comply with G98/G99. This guide covers every common cause, from high grid voltage and tripped MCBs to incorrect grid code settings.
Free remote diagnostic · pay only if we fix it — from £75 if remediable remotely
- H1 and H1-G2 all models
- No fix, no fee
- Not affiliated with Fox ESS
Grid fault keeping appearing?
Tell us the error code, the grid voltage reading, and how often the fault occurs. We diagnose Fox ESS grid issues remotely using Fox Cloud data and alarm histories.
Book your free remote diagnosticFox ESS hubIndependent — not affiliated with Fox ESS.
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
Geoffrey Heathcote · Jun 2026 Google
A really big thank you to Ron and his team, he has vast amounts of knowledge and got my system back up and running, also good to get on with. I was absolutely lost as to know what to do, no help from installer and somehow came across Ron and am I glad I did. I would definitely definitely recommend him to anyone who has faults with there solar system, any make I would say. Thanks again Ron a pleasure meeting you.
D R · Jun 2026 Google
This company are a rare gem, I had a very unusual problem following a failed firmware upgrade on my GivEnergy kit. I then found out GivEnergy were in administration and had dismissed all their support staff! None of the usual fixes to try and restore my inverter comms would work, and I looked everywhere, forums, GivEnergy youtube support videos - even AI couldn't figure it out. My installer was talking about huge sums for system replacements, and being vague / evasive about if they'd even install replacement GivEnergy inverter. Enter Solar Tech Support, reassuring and knowledgeable from the very start, I've learnt loads about my solar system though the friendly chat while my engineer worked as he diagnosed the problem and figured out a fix procedure that I've not found anywhere else - amazing. If you need solar system repairs - especially if you like me have been left high and dry by GivEnergy, I cannot recommend this company enough. Give them a call.
Andy Thomas · Apr 2026
Very very helpfuland so quick. Made sure that a non expert like myself understood what the problem was and how to resolve it.
Declan S · Jun 2026
I sent a message on their website regarding a problem I have on my Givenergy system. Although not supplied by Ronald, I thought it was worth an email. Within the hour on a Saturday, he phoned and we discussed the problem. He logged in remotely and gave excellent advice. I'm too far away for his on-site help but he did diagnose the problem and was happy also to chat through my thoughts about an upcoming solar/battery install I'm planning. Great bloke.... if only he was nearer!
Philip · Apr 2026
Before you start: open Fox Cloud and check the alarm history for the specific error code and the time it occurred. Also note the grid voltage reading on the inverter display or in Fox Cloud — this tells you immediately whether the fault is a genuine high-voltage issue or something else like a tripped breaker.
Diagnosis
Step-by-step grid fault diagnosis
Work through these steps in order. Step 2 catches the simplest cause — a tripped breaker. Steps 3 and 4 address the most common ongoing issues — high grid voltage and wrong settings.
1
Check Fox Cloud for the specific error code
Open Fox Cloud and check the alarm history. The key grid-related codes are: Error 1 (No Utility — no grid connection detected), Error 26 (Grid Voltage Fault — voltage outside permitted range), Error 27 (Grid Frequency Fault — frequency outside 49.5–50.5Hz), and Error 28 (10-Minute Average Voltage Fault — the rolling average has exceeded the upper limit). Note the code and the time it occurred — a midday-only pattern suggests solar export is pushing local grid voltage up.
2
Check whether the MCB or RCD has tripped
The inverter needs a live grid connection to operate. If the MCB feeding the inverter has tripped, it will report Error 1 (No Utility). Check the consumer unit for the circuit labelled Solar or PV and reset it if tripped. Fox ESS recommends: 20A MCB for 3.7kW models, 32A MCB for 5kW and 6kW models. If using an RCD or RCBO, it must be bi-directional and rated at 100mA, not 30mA — a standard 30mA device will nuisance-trip on normal inverter operation and cause repeated grid faults.
3
Check the grid voltage reading
The UK grid standard is 230V with a tolerance of +10% / -6%, giving a permitted range of 216V to 253V. Check the real-time grid voltage on the inverter display or in Fox Cloud. If the voltage consistently sits above 250V, the inverter will disconnect more frequently to comply with G98/G99 protection limits. High grid voltage is common in rural areas, at the end of long supply cables, and in streets with many solar systems exporting simultaneously. If readings regularly exceed 253V, the problem is with the grid supply, not the inverter — contact your DNO to report high voltage.
4
Verify the grid code settings are correct for the UK
The H1 must be configured to the correct UK grid code — G98 for installations exporting up to 3.68kW or G99 for larger systems. If the grid code is set to the wrong country or standard, the voltage and frequency protection limits will be wrong and the inverter may disconnect unnecessarily. Grid code settings are in the inverter menu under Settings → On-Grid → Grid Standard. This is normally set during commissioning, but firmware updates can occasionally reset it. Changing grid code settings requires the installer password.
5
Check AC wiring and connections
Loose or corroded AC connections between the inverter and the consumer unit can cause intermittent grid loss. The inverter sees a momentary voltage drop or spike as the connection makes and breaks, triggering Error 26 or Error 1. Check that the AC isolator switch is fully on and that there is no visible sign of heat damage or discolouration on cables or connectors. If you suspect a wiring fault, this must be checked by a qualified electrician — do not open the inverter or consumer unit yourself.
6
Power cycle the inverter and monitor
If the MCB is on, the voltage looks normal, and the settings are correct, perform a full power cycle: turn off the AC isolator, then the DC isolator, then the battery isolator. Wait 60 seconds. Turn them back on in reverse order — battery first, then DC, then AC. This clears transient grid faults and forces the inverter to re-measure the grid. If the fault returns within minutes, the grid voltage or frequency is genuinely outside limits — monitor the readings in Fox Cloud over 24 hours and contact STS for a remote diagnostic if the pattern continues.
Fox ESS grid faults — what you need to know
Every grid-connected inverter in the UK must comply with G98 or G99 grid protection requirements. These rules mandate that the inverter disconnects from the grid if voltage or frequency drifts outside safe limits — this protects both the local network and engineers who may be working on supply lines. The Fox ESS H1 does this correctly, so a grid code fault is not a defect — it means the inverter detected an abnormal grid condition and responded as required. The question is whether the grid condition is genuine or whether something else (a tripped breaker, loose wiring, wrong settings) is causing the inverter to see a false fault.
The most widespread genuine cause in the UK is high grid voltage. As more solar systems are installed on the same street, midday export pushes the local voltage upward. When it exceeds the G98/G99 upper threshold, every inverter on that circuit disconnects simultaneously — which paradoxically drops the voltage back down, allowing them to reconnect, creating a cycle. The long-term fix is for the DNO to adjust the local transformer tap or reinforce the network. STS can help by analysing your Fox Cloud voltage data over time, confirming whether the issue is grid-side, and providing the evidence your DNO needs to act. We are independent from Fox ESS and from your original installer.
Related Fox ESS guides
Cross-brand & guides
Grid faults — common questions
A grid voltage fault (Error 26) means the inverter has detected voltage outside the UK range of 216V to 253V. The most common cause is genuinely high grid voltage — particularly in rural areas or streets with many solar systems exporting simultaneously. The inverter disconnects to comply with G98/G99 protection. A tripped MCB or loose AC wiring can also cause voltage faults by interrupting the grid reference.
Error 26 is Grid Voltage Fault — measured voltage is outside the permitted range. Error 27 is Grid Frequency Fault — frequency has drifted outside 49.5–50.5Hz. Error 28 is 10-Minute Average Voltage Fault — the rolling average has exceeded the upper limit. All three are protection codes required by UK regulations. The inverter disconnects temporarily and reconnects automatically once conditions normalise. See the full Fox ESS fault code index for other codes.
On the inverter display, go to Settings → On-Grid → Grid Standard. The correct setting for most UK installations is G98 (up to 3.68kW export) or G99 (larger systems). If the code is wrong, voltage and frequency thresholds will be incorrect and the inverter may disconnect unnecessarily. Changing this setting requires the installer password. If a firmware update has reset it, contact STS or your installer to reconfigure.
The inverter protects itself by disconnecting when voltage exceeds limits, so sustained damage is unlikely. However, frequent disconnections mean lost generation and export income. If your grid voltage is consistently above 250V, contact your DNO — they have an obligation to keep supply within statutory range. In some cases the DNO can adjust the local transformer tap to reduce voltage across the area.
Repeated disconnections are usually caused by high grid voltage (especially midday when solar export peaks), a tripped or undersized MCB, or loose AC wiring causing intermittent voltage drops. Check Fox Cloud for the specific error code — Error 26 points to voltage, Error 27 to frequency, Error 1 to complete grid loss. If the fault is voltage-related and persists, contact STS — we can analyse your Fox Cloud voltage data and provide the evidence your DNO needs to investigate.
The remote diagnostic is free — we read your Fox Cloud voltage and alarm history and tell you whether the fault is grid-side, a settings issue, or wiring. If we can fix it remotely (for example correcting the grid code or G98/G99 settings) it is £75, and you only pay if we fix it. A genuine high-voltage supply problem is for your DNO to resolve at no cost to you, and we give you the data to evidence it. Wiring faults that need an electrician on site start from £245, quoted first.
Usually the same day. A grid code fault is normally confirmed in a single 30-minute remote session — we review your Fox Cloud voltage trend and alarm log while you describe how often the fault appears. You get a written summary of the cause and the recommended fix straight after the call, including the voltage evidence to send your DNO if the supply is out of range.
Book
Grid faults keep returning?
Tell us the error code, the grid voltage reading, and how often the fault occurs. We analyse Fox Cloud voltage and alarm data remotely to determine whether the issue is grid-side, settings-related, or a wiring fault. Independent from Fox ESS and your installer.
- Not affiliated with Fox ESS
- No fix, no fee
- On-site visits available across the UK
We use cookies to measure traffic and improve our ads — including sharing limited, hashed details with Meta (Facebook) to measure ad performance. Accept, or decline for essential cookies only. Privacy policy
STS Solar Tech Support
Usually replies within minutes
Hi there!
Got a solar fault or need a quick answer? Drop us a message — we usually reply within a few minutes. Mon–Fri, 9am–7pm.
Start WhatsApp Chat
Got a solar fault or need a quick answer? Drop us a message — we usually reply within a few minutes. Mon–Fri, 9am–7pm.
End-to-end encrypted