When your solar inverter displays an error code, it is telling you something is preventing normal operation. These codes range from temporary issues that clear themselves, such as brief grid fluctuations, to serious faults requiring professional attention. Understanding what common error codes mean helps you identify whether you are dealing with a minor issue you can address yourself or a problem that needs an engineer. The most frequent errors in UK systems relate to grid voltage being too high, isolation faults indicating potential wiring issues, and communication failures between system components.
Inverters use various methods to communicate faults: LED indicator lights that follow a traffic light pattern (green for normal, amber for warning, red for fault), display screens showing numeric or alphanumeric codes, and smartphone apps that log errors with timestamps and descriptions. Each manufacturer uses different code systems, but the underlying fault categories are similar across brands. Common categories include DC-side issues from the panels, AC-side issues relating to the grid connection, temperature problems, isolation faults, and communication errors.
This guide explains how to interpret error codes, covers the most common faults you will encounter with popular UK inverter brands, provides troubleshooting steps for issues you can safely address, and explains when professional help is needed. We also cover UK-specific considerations including G98/G99 grid code settings and when to contact your Distribution Network Operator (DNO) about grid voltage problems.
Quick Overview
| Most common UK fault | Grid over-voltage (high grid voltage) |
| Second most common | Isolation fault (insulation resistance low) |
| Indicator lights | Green = normal; Amber = warning; Red = fault |
| First step | Note the exact code, time, and conditions |
| Safe reset method | AC off first, then DC off, wait 5 minutes, DC on, then AC on |
| UK grid voltage range | 216V to 253V (230V nominal, +10%/-6%) |
| When to call professional | Persistent faults after reset; isolation faults; internal errors |
How Inverters Display Errors
Indicator Lights
| Light Colour | Typical Meaning |
|---|---|
| Solid green | Normal operation; generating power |
| Flashing green | Starting up or waiting for conditions |
| Amber/yellow | Warning; reduced operation; attention needed |
| Red | Fault; inverter stopped or in protection mode |
| Flashing red | Active fault requiring attention |
| No lights | No power; DC voltage too low; isolator off |
Display Screen
| Display Element | Information Provided |
|---|---|
| Error code number | Specific fault identifier (e.g., Error 203, E014) |
| Error message | Text description (e.g., “Grid Over-Voltage”, “Isolation Fault”) |
| Grid voltage reading | Current AC voltage; helps diagnose grid issues |
| DC voltage | Input from panels; indicates panel-side issues |
| Power output | Zero during fault; reduced during derating |
Monitoring Apps
| App Feature | How It Helps |
|---|---|
| Real-time status | Shows current fault codes remotely |
| Alarm history | Records all faults with timestamps |
| Voltage graphs | Shows patterns; helps identify recurring issues |
| Push notifications | Alerts you when faults occur |
| Remote reset | Some systems allow restart from app |
Error Code Categories
DC-Side Faults (Panel Side)
| Fault Type | Common Causes | Typical Codes |
|---|---|---|
| DC over-voltage | Too many panels in string; cold weather increases voltage | Varies by brand |
| DC under-voltage | Insufficient light; shading; panel fault; connection issue | Varies by brand |
| Isolation fault | Damaged cable insulation; moisture in connectors; ground fault | Error 203 (Growatt); E014 (Solis) |
| String fault | Broken connection; faulty panel; string mismatch | Varies by brand |
| Arc fault | Loose connection; damaged connector creating electrical arc | Safety shutdown |
AC-Side Faults (Grid Side)
| Fault Type | Common Causes | UK Relevance |
|---|---|---|
| Grid over-voltage | Grid voltage exceeds 253V; common in rural areas and high solar penetration areas | Very common in UK |
| Grid under-voltage | Grid voltage below 216V; less common | Less frequent |
| Grid over-frequency | Grid frequency exceeds 50.5Hz | Rare; grid usually stable |
| Grid under-frequency | Grid frequency below 47Hz | Very rare |
| No grid / utility loss | Grid power outage; tripped breaker; loose connection | Common during outages |
| Grid code fault | Inverter set to wrong country or G98/G99 setting | Configuration issue |
Temperature Faults
| Fault Type | Common Causes | Action |
|---|---|---|
| Over-temperature | Poor ventilation; direct sunlight; blocked heatsink | Improve airflow; shade inverter |
| Derating | Inverter reduces output to protect from overheating | Not a fault but reduces generation |
| Temperature sensor fault | Failed or disconnected sensor | Requires repair |
Communication Faults
| Fault Type | Common Causes | Action |
|---|---|---|
| WiFi/internet connection lost | Router issue; signal strength; dongle fault | Check network; reposition dongle |
| Meter communication fault | CT clamp issue; meter cable disconnected | Check connections |
| Battery communication fault | CAN bus error; BMS communication issue | Check battery connections |
| Optimiser communication | Optimiser offline; wiring fault | Check affected optimiser |
Internal Hardware Faults
| Fault Type | Meaning | Action |
|---|---|---|
| Relay fault | Output relay failure | Requires professional repair |
| IGBT fault | Power transistor failure | Requires professional repair |
| Current sensor fault | Internal sensor failure | Requires professional repair |
| EEPROM fault | Memory/firmware issue | May need firmware update or repair |
| Internal communication | SPI or bus failure | Requires professional repair |
Common Faults Explained
Grid Over-Voltage
This is the most common fault in UK solar systems. The inverter disconnects because the grid voltage exceeds the permitted upper limit (typically 253V in the UK). The inverter is doing exactly what it should: protecting itself and complying with G98/G99 grid code requirements. The fault often clears automatically when voltage drops back within range.
| Aspect | Details |
|---|---|
| UK voltage standard | 230V nominal; permitted range 216V to 253V |
| Common causes | Rural areas with long supply cables; areas with many solar systems exporting; time of day when demand is low |
| Pattern | Often occurs midday when solar generation peaks |
| Inverter response | Disconnects; auto-reconnects when voltage drops |
| Your action | Note frequency; if daily, report to DNO |
Isolation Fault
An isolation fault indicates the insulation resistance between the DC system (panels and cables) and earth/ground has dropped below the safe threshold. This is a safety-critical fault as it could indicate damaged cable insulation or moisture ingress, creating a potential shock or fire hazard. The inverter will not operate until the fault is cleared.
| Aspect | Details |
|---|---|
| What it means | Electrical leakage path between DC circuits and ground |
| Common causes | Damaged cable insulation; moisture in MC4 connectors; wet conditions; rodent damage |
| When it occurs | Often appears on rainy days or humid mornings |
| Severity | Safety-critical; do not ignore |
| Your action | If clears when dry, monitor; if persists, call professional |
| Professional action | Insulation resistance testing with megohmmeter to locate fault |
No Grid / Utility Loss
The inverter cannot detect grid power. This could be a genuine grid outage, but also occurs if a breaker has tripped, a fuse has blown, or there is a wiring fault on the AC side.
| Aspect | Details |
|---|---|
| Check first | Is there a power cut? Check other appliances |
| Check second | Has the solar AC breaker tripped in your consumer unit? |
| Check third | Is the AC isolator next to the inverter switched on? |
| If grid is present | Connection issue; loose wiring; call professional |
Inverter Not Turning On
A completely dark display with no indicator lights typically means insufficient DC power from the panels or a disconnection issue.
| Possible Cause | Check |
|---|---|
| Low light | Normal at dawn/dusk; inverter needs minimum voltage to start |
| DC isolator off | Check isolator switch on roof or near inverter |
| Tripped DC breaker | Check DC breaker if fitted |
| Panel issue | Snow cover; severe shading; disconnected cable |
| Inverter failure | If all above OK, inverter may have failed |
Error Codes by Brand
Different manufacturers use different code systems. For deeper coverage of each brand’s feature set, reliability, and warranty terms, our best solar inverters guide compares the leading UK options side by side.
GivEnergy
For a detailed look at the GivEnergy range, see our GivEnergy inverter review.
| Code/Message | Meaning | Action |
|---|---|---|
| Grid voltage high | Grid exceeds upper limit | Auto-recovers; report to DNO if frequent |
| Grid voltage low | Grid below lower limit | Auto-recovers; check connections if persistent |
| Isolation fault | DC insulation resistance low | Check for moisture; call professional if persists |
| Battery communication fault | CAN bus error with battery | Check battery cables; restart system |
| EPS fault | Emergency power supply issue | Check EPS wiring and configuration |
Solis
See our Solis inverter review for a full breakdown of this brand’s UK range.
| Code | Meaning | Action |
|---|---|---|
| E001-E005 | Internal communication errors | Reset; if persists, call professional |
| E011 | DC over-voltage | Check string configuration |
| E012 | DC under-voltage | Check panels and connections |
| E013 | DC over-current | Check for short circuit |
| E014 | Isolation fault | Check DC wiring insulation |
| E021-E025 | Grid voltage/frequency faults | Grid issue; auto-recovers normally |
| E031 | Relay fault | Internal fault; call professional |
Huawei
For Huawei’s product line, see our Huawei inverter review.
| Alarm ID | Meaning | Action |
|---|---|---|
| 2001 | High string voltage | Check string design; reduce panels if needed |
| 2002 | DC arcing | Safety shutdown; check all DC connections |
| 2011 | Grid over-voltage | Auto-recovers; contact DNO if frequent |
| 2012 | Grid under-voltage | Auto-recovers; check AC connections |
| 2031 | Low insulation resistance | Isolation fault; check DC wiring |
| 2061 | Abnormal grounding | Check PE cable connection |
| 2063 | Over-temperature | Improve ventilation |
SolarEdge
See our SolarEdge inverter review for details on the optimiser architecture and range.
| Error Type | Meaning | Action |
|---|---|---|
| Isolation fault (with code) | Ground fault in PV array | Check DC wiring; call professional |
| Grid voltage high | Grid exceeds country limit | Check country setting; contact DNO if correct |
| Over temperature | Inverter too hot | Check clearances; clean heatsink |
| AC voltage fault | Grid connection issue | Check AC wiring; consult grid operator |
| Ground fault | Current leakage to ground | Electrical shock hazard; call professional |
Fronius
For more on Fronius’s UK offering, see our Fronius inverter review.
| Class | Type | Action |
|---|---|---|
| Class 1 | Transient issues; grid fluctuations | Usually self-clearing |
| Class 3 | Temporary feed-in disruption | Short duration; auto-recovers |
| Class 4 | Requires installer intervention | Call accredited installer |
| Class 5 | Does not stop feed-in but restricts operation | Monitor; may need attention |
| State code 509 | No energy fed in last 24 hours | Check panels for dirt/shade; check connections |
| State code 314 | Current sensor calibration timeout | Usually self-clearing on restart |
Fox ESS
See our Fox ESS inverter review for this brand’s UK range.
| Fault | Meaning | Action |
|---|---|---|
| Grid code fault | Voltage or frequency outside G98/G99 limits | Check voltage; report to DNO if high |
| Grid over-voltage | Exceeds 253V | Auto-recovers; DNO issue if persistent |
| EPS fault | Emergency power issue | Check EPS configuration and wiring |
| Battery fault | BMS communication or battery issue | Check battery connections and status |
Growatt
| Code | Meaning | Action |
|---|---|---|
| Error 102 | CPU sampling error | Reset; monitor for recurrence |
| Error 111 | IGBT drive fault | Internal fault; call professional |
| Error 117 | Relay circuit problem | Try reset; call professional if persists |
| Error 120 | Current sensor fault | Internal fault; call professional |
| Error 203 | PV isolation fault | Check DC wiring; common in wet weather |
| Error 300 | AC voltage out of range | Grid issue; auto-recovers normally |
| Error 304 | Grid frequency fault | Grid issue; usually temporary |
SMA
For SMA’s UK product line, see our SMA inverter review.
| Code Range | Meaning | Action |
|---|---|---|
| 1302 | Grid fault | Check grid connection |
| 3501 | Insulation resistance (isolation fault) | Check DC wiring |
| 6002-6412 | Interference device / internal fault | May need replacement |
| 64xx series | Interference device errors | Internal fault; warranty claim if applicable |
UK-Specific Considerations
G98 and G99 Grid Codes
| Standard | Applies To | Relevance |
|---|---|---|
| G98 | Systems exporting up to 3.68kW per phase | Most residential systems |
| G99 | Systems exporting more than 3.68kW | Larger residential and commercial |
Inverters must be configured to the correct grid code for your installation. Wrong settings cause unnecessary disconnections or may not provide required protection. If your inverter shows grid code faults, check that the correct UK setting (G98 or G99) is selected, not a different country’s standard.
UK Grid Voltage Issues
| Issue | Details |
|---|---|
| Nominal voltage | 230V |
| Permitted range | 216V to 253V (+10%/-6%) |
| High voltage areas | Rural areas; end of long supply cables; areas with many solar systems |
| Peak problem times | Midday when solar generation peaks and demand is low |
| DNO contact | Report if voltage regularly exceeds 253V |
When to Contact Your DNO
| Situation | Action |
|---|---|
| Daily grid over-voltage faults | Report high voltage; DNO may adjust local transformer |
| Voltage consistently above 250V | Document readings; report to DNO |
| Frequent frequency faults | Unusual; report if pattern persists |
Troubleshooting Steps
Before You Start
| Step | Action |
|---|---|
| 1. Document the fault | Note exact code, time, weather conditions |
| 2. Check monitoring app | Review alarm history for patterns |
| 3. Check grid voltage | Note reading on inverter display |
| 4. Check for obvious issues | Tripped breakers; isolators switched off |
Safe Reset Procedure
| Step | Action | Why |
|---|---|---|
| 1 | Turn off AC isolator or breaker first | Disconnects from grid |
| 2 | Turn off DC isolator | Disconnects panel power |
| 3 | Wait 5 to 10 minutes | Allows capacitors to discharge; display should go dark |
| 4 | Turn DC isolator back on | Display should light up |
| 5 | Turn AC isolator/breaker back on | Reconnects to grid |
| 6 | Allow time for startup checks | Inverter runs self-tests before generating |
When Reset Clears the Fault
| Outcome | Interpretation | Action |
|---|---|---|
| Fault does not return | Likely transient issue (grid fluctuation, temporary condition) | Monitor; no further action unless recurs |
| Fault returns occasionally | Intermittent issue; may be environmental | Keep log; look for patterns |
| Fault returns immediately | Underlying problem not resolved | Do not keep resetting; call professional |
Checking Common Issues
| Issue | What to Check |
|---|---|
| No power at all | DC isolator; AC breaker; power cut; low light conditions |
| Grid voltage faults | Note voltage reading; check if within 216V-253V |
| Isolation fault in wet weather | May clear when dry; if persists when dry, needs investigation |
| Communication fault | WiFi signal; router status; cable connections |
| Low production | Shading; dirty panels; check individual string/optimiser status |
When to Call a Professional
Faults Requiring Professional Attention
| Fault Type | Why Professional Needed |
|---|---|
| Persistent isolation fault | Requires insulation testing equipment; safety critical |
| Arc fault | Fire risk; needs DC circuit inspection |
| Internal hardware faults | Relay, IGBT, sensor failures need repair or replacement |
| Repeated faults after reset | Underlying problem needs diagnosis |
| Ground fault warnings | Electrical shock hazard; do not touch equipment |
| Burning smell or visible damage | Turn off immediately; do not reset; call professional |
What Not to Do
| Action to Avoid | Reason |
|---|---|
| Opening inverter covers | Dangerous voltages inside; voiding warranty |
| Disconnecting MC4 connectors under load | DC arc flash risk; can cause burns and fire |
| Repeatedly resetting persistent faults | Masks underlying problem; may cause further damage |
| Ignoring isolation faults | Safety critical; could indicate fire or shock risk |
| Adjusting grid parameters without knowledge | May violate grid code; could cause unsafe operation |
Finding Help
| Option | When to Use |
|---|---|
| Original installer | First port of call; may be covered under workmanship warranty |
| Manufacturer support | For product faults; warranty claims |
| MCS-certified installer | If original installer unavailable |
| Solar maintenance company | For ongoing issues; system health checks |
Preventing Faults
Regular Checks
| Check | Frequency | Purpose |
|---|---|---|
| Visual inspection | Every 6 months | Check for damage, debris, obstructions |
| Monitor app review | Weekly or monthly | Check for logged faults; production patterns |
| Inverter ventilation | Every 6 months | Ensure heatsink and vents are clear |
| Panel cleaning | As needed | Prevents shading-related faults |
| Professional service | Annually recommended | Comprehensive check including electrical tests |
Optimising Inverter Location
| Factor | Recommendation |
|---|---|
| Ventilation | Ensure adequate clearance on all sides |
| Temperature | Avoid direct sunlight; excessive heat causes derating |
| Weather protection | Shield from rain if outdoor rated; ensure IP rating appropriate |
| Access | Easy access for maintenance and reading display |
Frequently Asked Questions
Basic Questions
| Question | Answer |
|---|---|
| Why is my inverter showing a red light? | Fault condition; check display or app for specific code |
| Will my inverter restart automatically? | For many faults (grid issues), yes; for others, manual reset or repair needed |
| How long should I wait before resetting? | 5 to 10 minutes minimum after turning off |
Grid Voltage Questions
| Question | Answer |
|---|---|
| Why does my inverter keep tripping on high voltage? | Local grid voltage exceeds 253V; common issue in UK |
| Can this be fixed? | Report to DNO; they may adjust transformer tap |
| Can the inverter be adjusted? | Only within G98/G99 limits by qualified installer |
Isolation Fault Questions
| Question | Answer |
|---|---|
| Why do I get isolation faults when it rains? | Moisture in connectors or damaged cable insulation |
| Is this dangerous? | Potentially yes; indicates current leakage path |
| What should I do? | If clears when dry, monitor; if persists, call professional |
Summary
| Aspect | Key Point |
|---|---|
| Most common UK fault | Grid over-voltage; auto-recovers; report to DNO if daily |
| Safety-critical fault | Isolation fault; do not ignore; call professional if persists |
| First step | Document code, time, voltage reading, conditions |
| Safe reset | AC off, DC off, wait 5 mins, DC on, AC on |
| Do not | Repeatedly reset persistent faults; open covers; touch DC connectors |
| Call professional | Persistent faults; isolation faults; internal errors; any safety concerns |
Inverter error codes are your system’s way of communicating problems. The most common fault in UK systems is grid over-voltage, where the local electricity supply exceeds the permitted 253V upper limit. This is particularly prevalent in rural areas, at the end of long supply cables, and in streets with many solar installations all exporting at the same time. The inverter disconnects to comply with G98/G99 grid protection requirements and typically reconnects automatically when voltage returns to normal. If this happens daily, document the issue and report it to your Distribution Network Operator, who may be able to adjust the local transformer.
Isolation faults are the second most common issue and the most important not to ignore. They indicate electrical leakage between your DC system and ground, potentially due to damaged cable insulation, moisture in connectors, or other wiring faults. These commonly appear during or after wet weather. If the fault clears when conditions dry out and does not return, it may indicate water ingress that needs monitoring. If the fault persists in dry conditions, professional diagnosis is essential as this represents a potential safety hazard.
For transient faults that clear after a single reset, no further action is usually needed beyond monitoring. For persistent or recurring faults, keep a log noting the code, time, weather conditions, and any patterns you observe. This information helps engineers diagnose the problem more quickly. Avoid repeatedly resetting an inverter that keeps faulting, as this may mask a serious underlying issue and could cause additional damage.
When in doubt, consult a professional. Internal hardware faults, repeated isolation errors, arc faults, and any situation where you smell burning or see physical damage require expert attention. Your original installer should be the first contact, but if they are unavailable, any MCS-certified solar installer can help diagnose and repair inverter issues.
Keep a simple log: date, exact code, grid voltage reading, weather. Two or three fault occurrences with the same pattern (e.g. “grid over-voltage, 254V+, sunny midday”) tell a DNO engineer more than a vague complaint. That data turns “my inverter keeps tripping” into “my local grid voltage is outside the permitted range at peak solar generation” – which is their problem to fix.
When you do call your installer, have your inverter make and model, system size, commissioning date, and the last 2-3 fault codes ready. Most good installers can diagnose a remarkable amount from that information alone without needing a visit.
