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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.
  • H1 and H1-G2 all models
  • Free remote-first diagnostic · 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.

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Independent — not affiliated with Fox ESS.

5.0
13 Trustpilot reviews
Trustpilot Google

I have a GivEnergy system consisting of two batteries, two inverters and a controlling EMS (Energy Management System) which has not worked since Nov 2025. After six months I discovered Solar Tech Support, reached out to them and Ron phoned me back – how often do you get that service? Could not be more helpful – worked directly with me over the phone, outside what I would call normal working hours. Lucid explanations and we were able to discuss the issues and history using camera and email history. As this was a very rare setup, Ron was able to access an EMS expert in the field to confirm the solution. One sunny day in, I am now only paying for standing charge and a few pence for spikes in grid consumption while battery catches up with house demand.

Ian · May 2026 Trustpilot

When my GivEnergy system had an issue, I was completely left without support and had honestly lost all hope. Thankfully, I searched online and found Ron, which completely turned things around. After sending him a message, he responded incredibly fast and called me to assure me that he would get the problem fixed. I really admire his dedicated, supportive nature and his determination to find a solution. With this kind of outstanding attitude and customer service, he has absolutely secured a future customer in me.

Sree · May 2026 Trustpilot

Ron want out of is way to help, nothing was to much. He was very thorough in what he did Very knowledgeable I would highly recommend Ron and his company He did a fantastic job for me. if you have any problems, he'll do his best to help you out and resolve your problem. I wouldn't hesitate to recommend them

Dennis Brown · May 2026 Trustpilot

Ron took me through a diagnostic to confirm my GivEnergy Inverter had a fault. A common one as it turns out with the AC Inverter. As GivEnergy is defunct there is no immediate fix, aside from sourcing 2nd hand replacement. It may be that a fix becomes available over the summer which would make a lot of GivEnergy customers happy (Again)

Tony Deacon · May 2026 Trustpilot

Contacted Ron with a problem and he sorted it out quickly with no problems at all. Very knowledgeable on anything solar/ batteries. I would recommend him to anyone

Phill · May 2026 Trustpilot

I've spoken to Ron a couple of times with issues with my Givenergy installation. Such a friendly knowledge guy very highly recommended. Thank you very much for resolving my issues

michael fairhurst · May 2026 Trustpilot

Contacted Solar Tech Support in desperation. After explaining the issues I had with my system a diagnosis was made and a solution proposed. Fantastic service, even contacted a manufacturer to arrange replacement parts for me. Great communications, explained all they were doing and what I had to do, clearly and precisly. Followed up to confirm all was ok. Excellent service.

Mr Machin · May 2026 Trustpilot

After GivEnergy went into liquidation, just my luck, my battery started playing up (internal board crashed). Contacted my installer - not interested! Found Solar tech support on a Google search. Sooo glad I found this company! Ron is extremely helpful and has plenty of experience. He soon confirmed what the fault was, and helped me to get my system up and running again. Now moved my GivEnergy account to Solar tech support, and will definitely use again if I have more issues. Unusual to find such a helpful company in these times, no morons reading scripts, just direct contact with the engineer.

Keith Ballard · Apr 2026 Trustpilot

Contacted Solar Tech Support when trying to understand what my Givenergy inverter problem might be and what might be my options. Received good/honest advise which backed up my thoughts.

Hugh Speirs · Apr 2026 Trustpilot

Ron is a super star. Two months ago my GivEnergy battery failed a firmware upgrade leaving it a brick. My installer couldn't/wouldn't fix it. GivEnergy couldn't/wouldn't fix it. Then they went into administration and all hope was lost. A flurry of emails later and Ron had diagnosed the fault (failed USB flash drive, something I'd suspected) and talked me through resolving it. Two months of nothing resolved in about 3 hours. It's great to work with someone who pays attention to the details, knows that they're doing (not just following a script) and gets stuff sorted without a fuss or up-charging.

Christopher · Apr 2026 Trustpilot

I can add to the list of customers who had already 'given up' on GivEnergy due to their appalling customer service, and that was before they went into administration (their Trustpilot reviews don't lie!). So you can imagine my desperation when, having changed my ISP and my Inverter, predictably, proving to be the only device that didn't connect automatically to my new network, I found zero prospect of any customer support with GivEnergy having called in the administrators just five days earlier! The salvation came from Solar Tech Support. My IT advisor stumbled across their web site and some very helpful tips for beleaguered GivEnergy customers, as well as an offer to provide direct assistance. Nothing ventured, I decided to drop them an E-Mail, with very low expectations based on my experience of GivEnergy customer support. Within an hour Ron had responded with some pin point advice, and after a few exchanges of E-Mails he had nailed the problem, enabling the combined efforts of my IT advisor and solar installer to resolve it and reconnect my Inverter. Thank you Solar Tech Support, and Ron in particular, for coming to the aid of a deserted and despondent GivEnergy customer. Expert, razor sharp advice and first class customer service, even though I wasn't officially a customer.

customer · Apr 2026 Trustpilot

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 Trustpilot

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 Trustpilot

I have a GivEnergy system consisting of two batteries, two inverters and a controlling EMS (Energy Management System) which has not worked since Nov 2025. After six months I discovered Solar Tech Support, reached out to them and Ron phoned me back – how often do you get that service? Could not be more helpful – worked directly with me over the phone, outside what I would call normal working hours. Lucid explanations and we were able to discuss the issues and history using camera and email history. As this was a very rare setup, Ron was able to access an EMS expert in the field to confirm the solution. One sunny day in, I am now only paying for standing charge and a few pence for spikes in grid consumption while battery catches up with house demand.

Ian · May 2026 Trustpilot

When my GivEnergy system had an issue, I was completely left without support and had honestly lost all hope. Thankfully, I searched online and found Ron, which completely turned things around. After sending him a message, he responded incredibly fast and called me to assure me that he would get the problem fixed. I really admire his dedicated, supportive nature and his determination to find a solution. With this kind of outstanding attitude and customer service, he has absolutely secured a future customer in me.

Sree · May 2026 Trustpilot

Ron want out of is way to help, nothing was to much. He was very thorough in what he did Very knowledgeable I would highly recommend Ron and his company He did a fantastic job for me. if you have any problems, he'll do his best to help you out and resolve your problem. I wouldn't hesitate to recommend them

Dennis Brown · May 2026 Trustpilot

Ron took me through a diagnostic to confirm my GivEnergy Inverter had a fault. A common one as it turns out with the AC Inverter. As GivEnergy is defunct there is no immediate fix, aside from sourcing 2nd hand replacement. It may be that a fix becomes available over the summer which would make a lot of GivEnergy customers happy (Again)

Tony Deacon · May 2026 Trustpilot

Contacted Ron with a problem and he sorted it out quickly with no problems at all. Very knowledgeable on anything solar/ batteries. I would recommend him to anyone

Phill · May 2026 Trustpilot

I've spoken to Ron a couple of times with issues with my Givenergy installation. Such a friendly knowledge guy very highly recommended. Thank you very much for resolving my issues

michael fairhurst · May 2026 Trustpilot

Contacted Solar Tech Support in desperation. After explaining the issues I had with my system a diagnosis was made and a solution proposed. Fantastic service, even contacted a manufacturer to arrange replacement parts for me. Great communications, explained all they were doing and what I had to do, clearly and precisly. Followed up to confirm all was ok. Excellent service.

Mr Machin · May 2026 Trustpilot

After GivEnergy went into liquidation, just my luck, my battery started playing up (internal board crashed). Contacted my installer - not interested! Found Solar tech support on a Google search. Sooo glad I found this company! Ron is extremely helpful and has plenty of experience. He soon confirmed what the fault was, and helped me to get my system up and running again. Now moved my GivEnergy account to Solar tech support, and will definitely use again if I have more issues. Unusual to find such a helpful company in these times, no morons reading scripts, just direct contact with the engineer.

Keith Ballard · Apr 2026 Trustpilot

Contacted Solar Tech Support when trying to understand what my Givenergy inverter problem might be and what might be my options. Received good/honest advise which backed up my thoughts.

Hugh Speirs · Apr 2026 Trustpilot

Ron is a super star. Two months ago my GivEnergy battery failed a firmware upgrade leaving it a brick. My installer couldn't/wouldn't fix it. GivEnergy couldn't/wouldn't fix it. Then they went into administration and all hope was lost. A flurry of emails later and Ron had diagnosed the fault (failed USB flash drive, something I'd suspected) and talked me through resolving it. Two months of nothing resolved in about 3 hours. It's great to work with someone who pays attention to the details, knows that they're doing (not just following a script) and gets stuff sorted without a fuss or up-charging.

Christopher · Apr 2026 Trustpilot

I can add to the list of customers who had already 'given up' on GivEnergy due to their appalling customer service, and that was before they went into administration (their Trustpilot reviews don't lie!). So you can imagine my desperation when, having changed my ISP and my Inverter, predictably, proving to be the only device that didn't connect automatically to my new network, I found zero prospect of any customer support with GivEnergy having called in the administrators just five days earlier! The salvation came from Solar Tech Support. My IT advisor stumbled across their web site and some very helpful tips for beleaguered GivEnergy customers, as well as an offer to provide direct assistance. Nothing ventured, I decided to drop them an E-Mail, with very low expectations based on my experience of GivEnergy customer support. Within an hour Ron had responded with some pin point advice, and after a few exchanges of E-Mails he had nailed the problem, enabling the combined efforts of my IT advisor and solar installer to resolve it and reconnect my Inverter. Thank you Solar Tech Support, and Ron in particular, for coming to the aid of a deserted and despondent GivEnergy customer. Expert, razor sharp advice and first class customer service, even though I wasn't officially a customer.

customer · Apr 2026 Trustpilot

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 Trustpilot

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 Trustpilot
ℹ️
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.

FAQ

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 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.
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
  • Free remote diagnostic · no fix, no fee
  • On-site visits available across the UK

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