Solar Inverter Error Codes Explained

What solar inverter error codes mean

Error and fault codes are brand-specific, and the exact string (a number, a letter prefix, or a short message) only means something in your own inverter's manual or app. But almost every code maps to one of a small set of general fault categories. Identifying the category usually tells you whether to wait, check something simple, or call for help. The list below is ordered roughly most-likely-first for a home system in Ireland.

1. 1. Grid faults (most common)

   Grid voltage too high or too low, grid frequency out of range, or grid loss (a power cut). Your inverter is legally required to disconnect when the grid moves outside set limits, so these codes often appear and clear on their own as the grid stabilises. A short power cut, or high voltage on a long rural feeder on a sunny afternoon, can both trigger them.

2. 2. Isolation / insulation resistance fault (ISO fault)

   The inverter has detected low insulation resistance somewhere on the DC side. In Ireland this is very often moisture-related: water ingress at a connector, a junction box, or a cable gland after wet weather. ISO faults frequently clear once everything dries out, but a code that keeps returning needs investigation by a qualified person.

3. 3. Earth / ground fault

   Closely related to an ISO fault: the inverter has sensed a leakage current to earth. This is a safety trip and should not be ignored if it persists. It usually points to a wiring or moisture issue on the array and is electrician territory.

4. 4. DC overvoltage

   The voltage coming in from the solar strings is above the inverter's maximum. This often shows up on cold, bright mornings when panel voltage peaks. A code that only appears occasionally in cold weather may be tolerable, but repeated DC overvoltage can indicate a string-design or wiring issue worth raising with your installer.

5. 5. Over-temperature

   The inverter is too hot and has throttled or shut down to protect itself. Common causes are a blocked vent, direct sun on the unit, or poor ventilation in a hot loft or cupboard. It usually recovers once it cools.

6. 6. Fan fault

   The internal cooling fan is blocked, failing, or reporting an error. The inverter may keep running with reduced output or shut down to avoid overheating. This is a hardware issue for your installer or a registered electrician.

7. 7. Arc fault (AFCI)

   The inverter's arc-fault detection has tripped, sensing a possible electrical arc on the DC side. Some can be reset once; a repeating arc-fault code should always be checked by a qualified person, as it is a fire-safety feature.

8. 8. Communication / meter fault

   A loss of communication with the monitoring app, the smart meter, an optimiser, or a battery. These rarely stop generation but break your monitoring. A power-cycle or reconnecting WiFi often fixes them; a wired meter or RS485 fault may need a technician.

Where to find your error code by brand

The exact code and its meaning live in your inverter's own app and manual. Record the exact code first, then look it up in the right place for your brand. Below are the major brands used in Ireland and where their codes are reported. For help choosing or comparing, see our solar inverter brands overview and our inverter comparison.

Because codes differ between brands and even between models, we don't list specific numeric codes here. Always confirm the exact meaning against your own inverter's manual or in-app fault description rather than assuming a code matches another brand's.

What you can safely check yourself

These steps are all app, display, breaker, and visual checks — nothing that involves opening the inverter or touching wiring. Work through them in order before calling anyone.

1. 1. Record the exact code

   Note the precise code or message shown on the inverter screen or in the app, and the time it appeared. A photo is ideal. This is the single most useful thing you can do, both for looking it up and for any call to your installer.

2. 2. Look it up in your brand's app or manual

   Open the relevant app (SolisCloud, FusionSolar, SEMS, mySolarEdge, and so on) and read the fault description, or check the inverter manual. This tells you which category the code falls into and whether it is self-clearing.

3. 3. Wait, if it is a grid fault

   Grid-related codes (voltage or frequency out of range, grid loss) often clear themselves once the grid stabilises or the power comes back. Give it some time, especially after a known outage or a very sunny spell, before doing anything else.

4. 4. Let an ISO fault dry out

   Isolation faults in Ireland are often triggered by moisture after rain. An ISO code that appears in wet weather and clears once things dry is usually nothing to act on. A code that keeps returning, or returns in dry weather, needs a professional.

5. 5. Check ventilation for a heat code

   For over-temperature, make sure nothing is blocking the inverter's vents and that the area around it is not baking in direct sun or trapped heat. Clearing space around the unit is safe and often enough.

6. 6. Reconnect monitoring for a comms fault

   For communication or meter codes that don't stop generation, re-checking your WiFi or re-pairing the app in the monitoring settings often restores the link without any other action.

7. 7. A controlled AC restart (only if your manual allows)

   Some manuals describe switching the inverter off and on again using the AC isolator switch (the labelled switch on the AC side, not anything on the DC side or inside the unit). Only do this if your manual says it is safe, and never open the inverter or operate the DC isolator under load.

Irish grid context: ESB Networks, NC6 and your supplier

Grid-related error codes are partly about the network your inverter is connected to. In Ireland, domestic solar is connected under ESB Networks rules, typically via the NC6 connection notice for small generators. Your inverter is set to disconnect if the local grid voltage or frequency drifts outside the permitted band, which is a safety feature, not a fault with your kit.

On long rural feeders, grid voltage can climb on bright afternoons when lots of local solar is exporting, which is a common reason for repeated high-voltage grid codes. If grid-voltage codes happen often and the inverter keeps cutting out, it is worth raising with your installer, who can take it up with ESB Networks if a network voltage issue is confirmed.

Separately, the Clean Export Guarantee (CEG) payments from your electricity supplier rely on your smart meter under the National Smart Metering Programme (NSMP). A communication or meter fault on the inverter affects your monitoring, but your export readings come from the ESB Networks smart meter, so a comms code does not by itself mean you have lost your export credit.

Frequently Asked Questions About Solar Inverter Error Codes

Related Guides

Sources

• ESB Networks: Generator connections (NC6 / microgeneration), esbnetworks.ie
• Safe Electric: Find a registered electrical contractor, safeelectric.ie
• SEAI: Solar Electricity Grant and registered contractors, seai.ie

Last updated: June 2026

Fact-checked by John Rooney, Solar Energy Editor. Editorial policy