Solar Inverter Error Codes: What They Mean and What to Do

You have spotted an error code on your inverter display, or your monitoring app has sent an alert. The good news is that most inverter faults are either self-resolving or straightforward to diagnose. The important thing is to know which category your fault falls into before you do anything at all.

This guide walks through what the most common error codes mean, which brands use which codes, and what action — if any — is yours to take.

How to find your error code

There are three places your inverter will tell you about a fault:

The front panel display. Most hybrid and string inverters have a small LCD or LED display. When a fault occurs, this will show either a text description (such as "Grid OV" or "Iso Fault") or a numeric code. Some older or budget inverters skip the display entirely and communicate only through LED colours.

The manufacturer's app. If your inverter is connected to your home WiFi, the monitoring app will usually show fault history, error codes, and sometimes an explanation. GivEnergy uses the GivEnergy app, Fox ESS uses the Fox Cloud app, SolarEdge uses the mySolarEdge app, Growatt uses ShinePhone, Solis uses SolisCloud, and Sunsynk uses the Sunsynk app.

LED light patterns. On inverters without a full display, the status LED tells you the broad category. Green typically means normal operation. Amber or orange indicates a warning — the inverter is still running but something is outside its normal range. Red means the inverter has shut down. Some brands use combinations of flashing patterns to communicate specific fault types; your inverter manual will have a legend.

Universal error categories

These fault types appear across most inverter brands — the exact code or label will differ, but the underlying cause is the same.

Grid voltage fault (Grid OV / Over-voltage)

Your inverter continuously monitors the voltage on the grid connection. UK regulations require the grid to stay between approximately 207V and 253V. When the voltage on your street rises above 253V — which happens most often on sunny afternoons when many nearby homes are simultaneously exporting solar power — your inverter is legally required to disconnect. This is a grid protection mechanism, not a fault with your equipment.

In most cases the inverter will reconnect automatically once the grid voltage drops back within range, usually within a few minutes. If you see this fault only occasionally and it clears itself, no action is needed beyond noting it in your log.

If grid over-voltage faults happen repeatedly — for example, most sunny afternoons — it is worth reporting the issue to your DNO (Distribution Network Operator). Your DNO owns the cables and substations in your area. They have a legal obligation under Engineering Recommendation G98 and G99 to maintain grid voltage within acceptable limits, and they can investigate whether the local network is being overloaded by solar export.

Grid frequency fault

Similar to voltage, the UK grid must operate at very close to 50Hz. If the frequency drifts outside the permitted range, your inverter disconnects automatically. This is rare and almost always self-resolves within seconds to minutes. If it happens frequently, it may indicate instability on your local grid section — again, a matter for your DNO rather than your installer.

Isolation fault / earth fault (Iso Fault / I-LEAK / RISO)

This is a more serious fault. The inverter has detected that the electrical insulation on the DC side of your system — the wiring between the solar panels and the inverter — has been compromised. This could be caused by:

• Water ingress into a cable junction box or MC4 connector (the weatherproof connectors joining panel cables)
• Physical damage to a cable from a bird, vermin, or roofing work
• Degraded insulation on an older cable exposed to UV and frost cycles
• A panel junction box that has cracked or delaminated

An isolation fault means electricity is finding a path to earth that it should not. This is both a shock risk and a potential fire risk. Do not reset and ignore an isolation fault. It needs a professional inspection of the DC wiring — typically using an insulation resistance test (Megger test) to locate the weak point. Your installer can do this.

Over-temperature (OT / Over Temp / Temp Fault)

The inverter has got too hot and has shut itself down to prevent internal damage. Before calling anyone, check:

• Is there adequate clearance around the inverter? Most manufacturers specify at least 200–300mm of clear space on all sides.
• Is the inverter mounted in a cupboard or enclosed space with poor airflow?
• Is it in direct sunlight for several hours a day?
• Are the ventilation slots blocked by dust, cobwebs, or stored items placed in front of it?

Clearing obstructions and improving ventilation will often prevent this fault from recurring. If the inverter is mounted in a loft or a south-facing utility room that gets very hot in summer, you may need to discuss repositioning with your installer.

DC arc fault (Arc Fault / AFD Fault)

This is the most serious fault on this list. A DC arc is an electrical spark occurring in the DC wiring — the wiring between your solar panels and the inverter. DC arcs burn at extremely high temperatures and are a leading cause of solar-related fires. Modern inverters include arc fault detection circuits (AFD) specifically to catch this.

Communication error (Comms Fault / BMS Com Fail / CAN Fault)

The inverter cannot communicate with another device in the system — typically the battery unit, a smart meter, or the monitoring gateway. These faults are usually caused by a loose data cable (CAN bus or RS485), a power cycle that left one device in a confused state, or a WiFi dropout affecting the monitoring connection only.

The inverter itself is often still generating power normally. Try power-cycling both the inverter and the battery (if applicable) in the correct sequence per your manufacturer's guidance. Check that any data cables between the inverter and battery are firmly plugged in at both ends. If the fault persists, your installer can reseat the connections.

String fault / MPPT fault

The inverter tracks maximum power from each string of solar panels using an MPPT (Maximum Power Point Tracker) circuit. A string or MPPT fault means one group of panels is not performing as expected. Possible causes include:

• A DC isolator that has been turned off (check the roof-mounted or wall-mounted isolator switches)
• Heavy shade on a portion of the array at the time of the fault
• A loose MC4 connector at a panel junction
• A failed panel or a bird strike causing physical damage

If the fault only appears at certain times of day and generation otherwise looks normal, shading is the likely explanation. If one MPPT consistently underperforms, it needs investigation.

Brand-specific common codes

Each manufacturer uses their own code system. The tables below cover the most common codes you are likely to encounter. If your code is not listed here, check your inverter manual or the manufacturer's online knowledge base.

GivEnergy

GivEnergy's official knowledge base at kb.givenergy.cloud lists all current fault codes with suggested remedies for each.

Fox ESS

The Fox ESS community forum at foxesscommunity.com is a useful resource for UK-specific fault discussions.

Solis

Sunsynk

Growatt

Growatt fault codes are further split into hardware faults (100-series), DC/PV side faults (200-series), and AC/grid side faults (300-series). This can help you identify which part of the system is involved before calling your installer.

SolarEdge

SolarEdge uses a different approach — faults are displayed as status codes grouped by type.

SolarEdge also displays P-series optimiser faults on individual panel strings, visible in the mySolarEdge app's layout view. If one panel shows as offline consistently, the power optimiser on that panel may have failed.

What you can safely do yourself

There are a handful of steps that are genuinely yours to take before calling a professional.

Restart the inverter. This is the closest thing to an official first step for most transient faults. Turn off the AC isolator (on your consumer unit), then turn off the DC isolator (usually mounted on the wall near the inverter). Wait five minutes — this allows internal capacitors to discharge and the grid voltage to stabilise. Then restore power: DC isolator first, then AC isolator. Many one-off grid faults and communication glitches clear after a restart.

Check all isolators are switched on. It sounds obvious, but after maintenance work, a power cut, or an RCD trip, an isolator can be left in the off position. Confirm both the DC and AC isolators are fully in the on position.

Check ventilation. Clear any obstructions from around the inverter. Remove any items stacked in front of it. Check that ventilation slots are not clogged with dust — a soft brush or vacuum can clear these externally without opening anything.

Check the WiFi connection. Communication faults in the app are sometimes just a dropped WiFi connection. Check whether your inverter's WiFi dongle or data logger is connected (usually indicated by a light on the device). Restarting your router can resolve these.

Check your app for fault history. Most monitoring apps show a log of faults with timestamps. This can tell you whether the fault is new, recurring, or intermittent — all useful information for your installer.

What you should not do

Do not open the inverter casing. The internal components operate at voltages that can be lethal even with isolators switched off. Stored charge in capacitors can persist for several minutes. Inverter casings are also sealed to protect against moisture ingress — opening one can void your warranty even if you close it again.

Do not touch DC wiring. The cables running from your solar panels to the inverter carry DC voltage at whatever the panels are producing — which on a bright day can be several hundred volts. Unlike AC wiring, there is no way to interrupt DC from the panels by switching a breaker at the consumer unit. The only way to de-energise the DC side is to disconnect the panels themselves, which requires working on the roof.

Do not reset a DC arc fault. As noted above, this is the one fault type where repeated resets are genuinely dangerous. If the arc fault detection has triggered, the fault needs to be found and fixed before the system is energised again.

Do not ignore a fault that keeps returning. A one-off grid over-voltage fault that self-resolves is unremarkable. The same fault appearing every sunny afternoon, or any isolation or arc fault that reappears after a restart, is a signal that something needs professional investigation.

Recording errors for your installer

When you call your installer to report a fault, the more specific information you can give them, the faster they can diagnose it. Before you pick up the phone:

• Screenshot or photograph the error code on the display or in the app
• Note the exact time the fault appeared — to the nearest minute if possible
• Note the weather conditions — sunny, overcast, raining, overnight
• Note whether the fault cleared itself and if so, how long it took
• Check whether the fault has appeared before — look back through your app's history
• Note any other context — was there a power cut in your street, did a contractor do any work recently, did you notice anything unusual?

This information allows your installer to quickly distinguish between a transient grid event, a developing insulation issue, or an internal inverter problem. It can also be crucial for warranty claims — manufacturers often want evidence that a fault was logged before parts are replaced under warranty.

If your system is still within its installer warranty period (typically 1–2 years from installation) or within the manufacturer's inverter warranty (typically 10 years), make sure you contact the right party. For workmanship issues, contact your original installer. For a confirmed hardware fault, your installer will liaise with the manufacturer on your behalf.

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