Solar Inverter Troubleshooting: Common Faults and How to Fix Them

When your solar inverter is not working, the first instinct is to assume the worst. In practice, a significant proportion of apparent solar inverter faults are caused by external factors that have nothing to do with the inverter itself: a tripped breaker, a switched-off isolator, or a brief grid disturbance that has cleared on its own. This solar inverter troubleshooting guide walks through the ten most common faults in order of frequency, gives you a clear three-step diagnostic sequence to work through before anything else, and provides brand-specific error code tables for SolarEdge, Enphase, Fronius, and Growatt. By the end, you will know exactly what you can check yourself and, just as importantly, what requires a qualified engineer.

Start Here: Three Checks Before Anything Else

Before investigating any specific fault code or symptom, work through these three checks in order. They resolve a surprising number of apparent inverter failures without any further diagnosis.

• Check the AC and DC isolators are ON. Your system has a DC isolator (between the panels and the inverter, usually on the wall near the unit or on the roof) and an AC isolator (between the inverter and the consumer unit). Both must be in the ON position for the inverter to operate. Either can be switched off accidentally during other work in the area, such as decorating, loft access, or electrical work elsewhere in the property.
• Check the solar PV breaker in your consumer unit. The solar generation circuit has its own MCB (Miniature Circuit Breaker) in the consumer unit, labelled Solar, PV, or Generation on most installations. If this has tripped, the inverter cannot export power. Reset it once: if it holds, the issue may have been transient. If it trips immediately again, do not force it: call an engineer.
• Check your monitoring app for error codes. Before looking at the physical unit, open the SolarEdge monitoring portal, Enphase Enlighten, Fronius Solar.web, or the Growatt ShinePhone app (whichever applies to your system). The app will show the most recent fault, the time it occurred, and whether it has self-cleared. This information gives both you and any engineer a significant head start on diagnosis.

If all three checks are clear and the inverter is still not generating during daylight hours, the fault is inside the system. Continue with the fault guide below.

Understanding Your Solar Inverter Status Lights

Every inverter uses indicator lights or a digital display to communicate its operating state. While colour coding varies slightly between brands, the following conventions are broadly consistent across UK residential inverters.

• Solid green: Normal operation. The inverter is generating and exporting power to your home and grid.
• Flashing green: Starting up, usually seen in the first few minutes after sunrise as the inverter locks onto the grid.
• Solid or flashing amber/yellow: Warning state. The inverter is operational but has detected a condition worth monitoring. Common causes include a grid voltage event that has self-cleared, or a low-priority sensor reading outside the expected range.
• Solid red: Active fault. The inverter has shut down and cannot generate. A fault code will be displayed or available in the monitoring app.
• No lights, blank display: The inverter has no power supply. This is almost always caused by a tripped AC breaker or an off AC isolator rather than an inverter failure.

Quick reference: A blank display during daylight hours is rarely caused by a dead inverter. Check the AC isolator and consumer unit first.

The 10 Most Common Solar Inverter Faults

Fault 1: Solar Inverter Not Producing Power (Zero Output)

Zero output is the most alarming symptom and, counterintuitively, often the easiest to resolve. The inverter display shows 0W or a standby state during full daylight, and the monitoring app confirms no generation for an extended period.

Why does my inverter show 0W output? The most common causes, in order of frequency:

• AC isolator is off or consumer unit breaker has tripped. Already covered in the three-step check above. Resolve this before any further investigation.
• Grid outage or sustained grid under-voltage. During a grid outage, all grid-tie inverters disconnect automatically for anti-islanding safety. They will not restart until the grid has been stable for several minutes after power returns. Check whether neighbours have power.
• Inverter in night mode. Inverters do not generate in darkness and switch to a low-power sleep mode. This is correct behaviour. If the unit is in night mode during the day, the DC input voltage from the panels is below the inverter’s start-up threshold, which points to a DC circuit fault or severe shading.
• Active fault code causing shutdown. Check the display and monitoring app for a specific error code, then cross-reference against the error code tables in this article.
• Communication failure between panels and inverter. Particularly relevant for microinverter systems where an Envoy gateway communication fault can prevent the app from showing generation even if panels are producing. Check the gateway status light.

Important: A string inverter showing 0W with a blank display and no response to the power button, combined with confirmed live AC and DC supplies, indicates a hardware failure inside the unit. This requires an engineer.

Fault 2: Grid Over-Voltage Fault

A grid over-voltage fault is the single most common solar inverter fault code reported in the UK. It accounts for a large proportion of all inverter trips in residential solar PV systems, particularly in areas with high concentrations of solar generation on the local distribution network.

What happens: the local grid voltage at your connection point rises above the G98 upper threshold (nominally 253V at the point of connection). The inverter detects this, disconnects from the grid as required by regulation, displays an over-voltage or AC high fault code, then waits for the voltage to return to an acceptable level before reconnecting. On most days, this cycle resolves within minutes and leaves no lasting effect.

When it becomes a problem: if the local grid voltage is consistently elevated, the inverter may trip and reconnect repeatedly throughout the day, losing a significant proportion of potential generation. This is a Distribution Network Operator (DNO) issue rather than an inverter fault, but it is the inverter that shows the symptom.

What to do:

• Note the frequency of the fault in your monitoring app. Most portals show fault frequency history.
• If the fault occurs more than ten times per week or causes extended periods of zero generation, report it to your DNO as a power quality complaint.
• A qualified engineer can review the G98 voltage trip threshold settings in your inverter and, in some cases, adjust the voltage threshold within permitted limits to reduce unnecessary tripping.

Context note: Grid over-voltage faults increase in summer when generation across the local network is highest. A system that trips occasionally in June and July but runs cleanly the rest of the year is behaving normally. A system that trips daily throughout the year needs investigation.

Fault 3: Isolation Fault (Insulation Resistance Low)

An isolation fault, sometimes displayed as insulation resistance low, GFDI fault, or ground fault, indicates that the DC wiring in the primary circuit has developed an unintended electrical connection to earth. This is a safety-critical fault: it indicates damaged cable insulation, a moisture ingress point in a junction box, or a panel with a compromised internal connection.

All modern solar inverters test the insulation resistance of the DC circuit before connecting to the grid each morning. If the measured resistance falls below a safe threshold (typically around 1 MOhm on residential systems), the inverter locks out and displays an isolation fault.

Critical safety note: An isolation fault code must never be cleared and reset without a full DC circuit inspection by a qualified engineer. The fault exists for a safety reason. Operating a system with an active isolation fault creates a shock risk and a fire risk from DC arcing. Do not attempt to reset an isolation fault yourself.

Engineers investigating isolation faults typically carry out:

• String-level insulation resistance testing to identify which string contains the fault.
• Panel-level inspection to identify any physically damaged panels, water ingress in junction boxes, or compromised cable connectors.
• DC cable inspection for rodent damage, UV degradation, or mechanical damage at roof penetration points.

Fault 4: Solar Inverter Overheating

Solar inverter overheating causes an automatic thermal protection shutdown. The inverter will display an overtemperature or high temperature fault code, shut down, and restart once the internal temperature falls back within operating limits. Repeated overheating cycles shorten the operational life of the inverter significantly.

Common causes:

• Blocked ventilation clearances. Items stored against the inverter, a closed cupboard with no airflow, or a loft installation where ambient temperatures regularly exceed 40 degrees Celsius.
• Failed cooling fan. Many string inverters use an internal fan to assist heat dissipation at higher power output levels. A seized or failing fan reduces cooling capacity significantly. The fan fault is usually accompanied by or preceded by unusual noise.
• Excessive ambient temperature. Loft spaces in South England reach 50 to 60 degrees Celsius on hot summer days. This is outside the specified operating range of most residential inverters.
• Dust accumulation on heat sink fins. Older inverters in dusty environments can develop a layer of insulating dust on their external heat sink surfaces, reducing passive cooling effectiveness.

For a homeowner: check that the inverter has the manufacturer’s recommended clearances on all sides, confirm the fan outlet is unobstructed, and consider whether a loft installation should be relocated if overheating is a recurring issue.

Fault 5: Solar Inverter Making Noise

Some noise from a solar inverter is entirely normal. Understanding which sounds are normal and which indicate a developing fault can save significant cost if problems are caught early.

• Normal sounds: a gentle electrical hum during operation (transformer magnetostriction), quiet fan airflow at full output on hot days, and a relay click when the inverter connects to the grid in the morning or disconnects at sunset.
• Abnormal sounds requiring investigation: loud continuous buzzing that has recently increased in intensity (transformer saturation or resonance, sometimes caused by grid voltage distortion); grinding, rattling, or intermittent mechanical noise (fan bearing failure); clicking or ticking at irregular intervals (relay cycling due to repeated grid connection attempts, pointing to a grid quality fault).

A fan bearing failure is worth attending to promptly. The fan is a replaceable component on most inverter models. Continuing to operate an inverter with a seized fan risks the thermal protection shutdown sequence described above, and sustained high-temperature operation accelerates the degradation of electrolytic capacitors inside the unit.

Fault 6: Solar Inverter Keeps Tripping the Breaker

If the solar PV circuit breaker in your consumer unit trips repeatedly, the inverter is either drawing abnormal current on the AC output side, or there is a fault in the AC wiring between the inverter and the consumer unit.

Common causes:

• An AC wiring fault at the inverter connection or at the consumer unit itself: this requires an electrical inspection.
• An inverter output fault causing a current spike that exceeds the MCB rating: this requires the inverter to be assessed by an engineer.
• An incorrectly rated MCB: if the MCB was not sized correctly at installation, it may trip under normal generation current. This is an installation deficiency rather than an inverter fault.

Important: Do not repeatedly reset a circuit breaker that keeps tripping. A circuit breaker that trips on every reset is protecting the circuit from a real fault. Each forced reset drives fault current through the wiring and can cause thermal damage to cables or connectors over time.

Fault 7: Low Output Without a Fault Code

A system that is generating but consistently underperforming relative to its rated capacity, with no active fault code, is one of the more frustrating diagnostic scenarios. The inverter appears to be working normally, but generation figures are noticeably lower than expected.

Common causes in order of likelihood:

• Soiling on panels. A layer of dust, bird droppings, or lichen on the panel glass reduces light transmission. Panels in rural areas, near arable farmland (pollen and dust), or heavily used by birds can lose 5 to 20 percent of output to soiling.
• New shading. Tree growth, a new dormer window, a neighbouring extension, or a recently installed satellite dish may be casting shadows on panels that were unshaded at installation.
• MPPT degradation in older inverter. Aging inverters may show reduced MPPT tracking accuracy before other fault symptoms appear. The generation shortfall is consistent but not catastrophic.
• Panel degradation. Panels degrade at approximately 0.5 percent per year under normal conditions. After ten to fifteen years, this cumulative degradation is measurable in generation data.
• String configuration fault. A failed bypass diode within a panel can cause that panel to act as a resistive load on the string, reducing overall output even when the panel appears physically intact.

Fault 8: Solar Inverter Display Not Working

A blank or unresponsive inverter display during daylight hours is almost always caused by a loss of AC power to the inverter rather than a display fault. Work through the three-step check at the top of this article: AC isolator position, then consumer unit MCB, then monitoring app.

If the AC supply to the inverter is confirmed live and the display remains blank, the inverter has a power supply fault internally. On some inverter models, the display is separately powered from the main AC input and can fail independently, leaving the inverter generating normally but with no visible status. Check the monitoring app: if generation data is visible and normal, the fault is the display module alone. If the app shows no generation either, the entire unit has lost power or failed.

Fault 9: Inverter Trips in the Morning and Recovers Later

An inverter that faults repeatedly in the early morning and then runs normally once the day is underway is exhibiting a specific pattern that points to one of two causes.

Grid over-voltage in morning peak. In many UK residential areas, grid voltage is highest in the early morning before commercial demand draws it down. Solar generation from multiple systems in the street also elevates grid voltage. The inverter trips at connection, waits, retries, and eventually connects when grid voltage has stabilised. This is a DNO grid quality issue.

Dew or condensation affecting DC circuit insulation. An isolation fault caused by moisture will typically be most pronounced in the early morning when dew is present on panels and in roof-level junction boxes, and will clear as the system warms up and moisture evaporates. If the morning trip is accompanied by an isolation fault code, this is the more likely cause.

Diagnostic tip: Check whether morning trips occur on specific days (cold, damp mornings) or every day regardless of weather. Weather-correlated morning faults strongly suggest a moisture-related isolation issue. Non-weather-correlated morning faults point to grid voltage.

Fault 10: Intermittent Operation and Unexplained Shutdowns

An inverter that works normally for hours or days then shuts down without a consistent trigger, with no obvious fault code or clear environmental cause, is one of the most challenging faults to diagnose remotely. The most common underlying causes are:

• Degraded capacitors. As electrolytic capacitors age, their capacitance and ESR (equivalent series resistance) degrade. The symptoms can be highly intermittent: the inverter functions normally under light load but fails under sustained generation. Capacitor replacement is a component-level repair that requires an engineer.
• Loose or corroded DC connector (MC4 connector). MC4 connectors are the standard push-lock DC cable connectors used at panel and string level. A connector that has not been properly latched, has corroded, or has developed a high-resistance joint can cause intermittent disconnection at the DC input. High-resistance MC4 connections also generate heat and represent a fire risk.
• Failing internal relay. The relay that connects the inverter output to the grid has a finite number of switching cycles. A relay approaching end of life may produce intermittent connection failures before failing completely.

How to Reset a Solar Inverter

A soft reset of a solar inverter should only be attempted after checking the three-step sequence at the start of this article, and only when the fault code displayed is a recoverable warning rather than a safety-critical fault (such as an isolation fault or arc fault code).

The standard reset procedure for most UK residential inverters:

• Switch off the AC isolator between the inverter and the consumer unit.
• Switch off the DC isolator between the panels and the inverter.
• Wait two minutes to allow the inverter’s internal capacitors to discharge fully.
• Switch the DC isolator back ON.
• Switch the AC isolator back ON.
• Allow the inverter three to five minutes to complete its startup and grid connection sequence.

The inverter should display its normal startup sequence and reconnect to the grid. If it shows the same fault code immediately on restart, or if a new fault code appears, do not continue resetting. The fault is persistent and requires professional diagnosis.

Do not reset these faults: Isolation faults (insulation resistance low, GFDI, ground fault), arc fault codes (AFCI), and hardware fault codes should never be cleared by a homeowner reset. These codes indicate conditions that are safety risks. Call an engineer before attempting any reset.

Brand-Specific Error Code Reference Tables

The following tables cover the most commonly encountered error codes for the four most widely installed inverter brands in the Solar Maintenance And Repairs service area. For fault codes not listed here, consult your inverter manufacturer’s documentation or call Solar Maintenance And Repairs technical support line.

SolarEdge Error Codes

Enphase Microinverter Status Reference

Fronius Inverter Error Codes

Growatt Inverter Error Codes

How to Tell If Your Solar Inverter Is Faulty vs Just Switched Off

This is one of the most common questions engineers receive, and the distinction matters because the response is completely different.

Signs the inverter is switched off but otherwise healthy:

• Blank display, no lights, no response to the power button.
• AC isolator is confirmed in the OFF position, or consumer unit MCB has tripped.
• Monitoring app shows no generation but no active fault code.
• Generation resumes immediately and normally when the isolator or MCB is restored.

Signs the inverter has an active fault:

• Red LED or fault code on display during daylight with isolators confirmed ON.
• Monitoring app shows a specific fault code with timestamp.
• Inverter attempts to connect and immediately disconnects, cycling repeatedly.
• Inverter display is active (backlit, showing temperatures or voltages) but not generating.

Signs the inverter has failed permanently:

• No response to power after confirmed live AC and DC supplies.
• Burning smell, discolouration, or visible damage on the unit exterior.
• Hardware fault code that persists across multiple reset attempts.
• Internal buzzing or crackling sounds combined with zero generation.

Expert Insights: Patterns Engineers Find in the Field

Solar Maintenance And Repairs NAPIT-registered engineers carry out solar inverter diagnostic visits and repairs across Hampshire, Surrey, Kent, Dorset, West Sussex, and across the wider South England service area. The following patterns come directly from repeated field experience.

Grid Over-Voltage Is Vastly Underdiagnosed

The majority of homeowners who report an intermittently underperforming system have never checked their inverter monitoring logs for grid over-voltage events. Engineers regularly find that a system described as ‘not working properly’ has been tripping on grid over-voltage twenty to forty times per day, losing two to four hours of generation daily, for months or years. The homeowner’s energy bills have been higher than necessary throughout this period, and the solution is a five-minute DNO report and, in some cases, a threshold adjustment in the inverter settings. This fault is completely invisible without monitoring data, which is why checking the app is step three of the initial diagnostic sequence.

MC4 Connector Failures Are a Fire Risk That Goes Unnoticed

High-resistance MC4 connector faults do not always produce an obvious fault code. The resistance at the connector reduces the DC current below the string’s rated output, which the inverter often interprets as reduced irradiance rather than a wiring fault. The connector meanwhile heats up, sometimes to the point of melting the plastic housing or scorching the cable. Solar Maintenance And Repairs engineers have found MC4 connectors on UK roofs in a severely degraded state, with evidence of sustained arcing and thermal damage, on systems that showed only a modest generation shortfall and no active fault codes. Thermal imaging of roof-level DC connectors during a service visit catches these before they escalate.

Monitoring Apps Are Left Dormant for Years

A recurring finding: a homeowner calls about a problem, and the monitoring app shows a fault that started six, twelve, or eighteen months earlier. In some cases, the system has been offline for that entire period and the household has been drawing full mains power, unaware that their solar generation had completely stopped. The missed generation represents a tangible financial loss. Setting up monitoring alerts, as described in the professional recommendations section, converts an app that most homeowners rarely open into an automatic watchdog that notifies you within hours of any fault.

Common Mistakes During Solar Inverter Troubleshooting

Repeatedly Resetting Without Diagnosing

When the inverter displays a fault code, the temptation is to reset it and see if the problem goes away. A reset that clears the fault temporarily and allows generation to resume for a few hours gives a false sense that the problem is solved. Each reset without diagnosis delays the identification of an underlying fault that is typically worsening over time. An isolation fault that clears on reset in July and is left unaddressed may have progressed to a full DC wiring failure by October.

Assuming Reduced Output Means the Inverter Is Failing

Reduced generation output is the most common reason homeowners contact engineers about an apparent inverter fault, and in the majority of cases the inverter is working correctly. Soiling on panels, new shading, and seasonal irradiance variation account for the vast majority of generation shortfalls. Before concluding the inverter needs attention, clean the panels, check for new shading obstructions, and compare generation against the equivalent month in the previous year rather than against a recent sunny period.

Searching for Error Codes from a Different Brand

Error code numbering is not standardised across inverter manufacturers. Error 02 on a Growatt inverter means something entirely different from error 02 on a Fronius. Homeowners who search for a fault code without specifying the brand frequently find information that does not apply to their system. Always include the inverter brand in any search, and use the brand-specific tables in this article as the starting reference.

Calling an Engineer for a Tripped Breaker

A significant proportion of solar inverter call-outs turn out to be a tripped consumer unit MCB or a switched-off isolator. Both are ten-second fixes that a homeowner can perform safely. Working through the three-step check at the start of this article before booking an engineer call-out saves both time and cost.

Industry Best Practices for Preventing Inverter Faults

• Configure monitoring alerts in your inverter app. Push notifications for generation shortfalls and fault codes give you same-day awareness of problems that might otherwise go undetected for weeks.
• Check your inverter display or monitoring data monthly. Record the cumulative generation figure and compare it month-on-month and year-on-year to catch slow degradation.
• Keep ventilation clearances maintained throughout the inverter’s life. The garage or utility room that was clear at installation may have accumulated items that now restrict airflow.
• Schedule a professional inverter health check alongside your solar panel service. Thermal imaging of roof-level DC connectors, DC insulation testing, and MPPT performance assessment are checks that require professional equipment but can be combined with a standard service visit.
• Do not ignore recurring error codes that self-clear. If an error appears and clears daily, or weekly, note the code and the frequency and report it to a qualified engineer. Self-clearing faults indicate an intermittent condition that will eventually become permanent.
• Keep installation documentation including the inverter make, model, and serial number in a accessible location. This information is needed for warranty claims and for an engineer to confirm the correct replacement unit before attending site.

When to Call a Solar Inverter Engineer

Some faults are straightforward homeowner checks. Others require professional equipment and qualifications. The following situations always require a qualified engineer:

• An isolation fault, GFDI, or ground fault code. These are safety-critical faults that create shock and fire risk. Never reset without professional inspection.
• An AFCI or arc fault code. Arc faults in DC wiring can cause fires. Treat them as urgent.
• A consumer unit MCB that trips on every reset attempt. A persistent trip indicates a real fault in the wiring or inverter output stage.
• Burning smell, discolouration, melted plastic, or any sign of thermal damage on or near the inverter.
• Zero generation that persists after completing the three-step check with all isolators confirmed in the ON position.
• Recurring fault codes that you cannot identify or that return repeatedly within hours of resetting.
• A system where the inverter has not been serviced or assessed in more than five years.

Solar Maintenance And Repairs provides solar inverter diagnostic call-outs, repair, and replacement services across Hampshire, Surrey, Kent, Dorset, West Sussex, East Sussex, Wiltshire, Berkshire, Somerset, Devon, and all other counties in the South England service area. Our NAPIT-registered and Trustmark-endorsed engineers carry diagnostic equipment and commonly required replacement parts to most visits.

Conclusion

Solar inverter troubleshooting does not always require an engineer. Many of the most common faults, including grid over-voltage trips, tripped breakers, and switched-off isolators, can be identified and resolved by a homeowner who knows where to look and what to check. This guide has given you the complete framework: the three-step initial check, the ten most common fault patterns with their causes and responses, brand-specific error code tables for the four most widely installed inverter brands, and a clear set of criteria for when professional help is required.

The most important habit you can develop as a solar PV system owner is routine monitoring. A generation shortfall that is caught within a day costs nothing. A fault that has been running silently for six months costs weeks of lost generation and, in the worst cases, accelerated component damage. Configure your monitoring alerts today if you have not already done so.