Solis Inverter Fault Codes: What They Mean and What to Do

Most Solis alarm messages tell you where the problem is: the grid, the solar panels and their wiring, or the inverter’s own electronics. Grid alarms usually clear by themselves once the mains supply is back within limits. Insulation, leakage and internal alarms need an engineer, especially if they keep coming back.

This guide uses the alarm names in Solis’s published list of alarm messages for its grid-tied and energy storage (hybrid) inverters. Names and codes can vary by model and firmware, so the manual for your inverter is the final word. Solis is clear that diagnosis and repair are for trained electricians, not homeowners.

Key points

• Grid alarms (NO-Grid, OV-G-V, UN-G-V, OV-G-F, UN-G-F) mean the inverter has disconnected to protect the network. It reconnects when the grid is back to normal.

• PV ISO-PRO and ILeak-PRO point to an insulation or earth leakage problem on the solar side. One in the early morning or after rain can clear; repeats need an engineer.

• OV-TEM means the inverter is too hot. Ventilation and direct sun are the usual suspects.

• Battery and meter communication alarms on hybrid systems explain a lot of odd battery behaviour.

• Never open the inverter or battery, and don’t switch DC isolators unless an engineer has told you how and in which order.

First: is the alarm still showing?

Check the inverter screen or the SolisCloud app and see whether the alarm is active now or only in the history. Many alarms are logged, clear within minutes and never return. Write down the exact message, the date and time, and whether it keeps coming back. Photograph the label on the side of the inverter with the model and serial number. That is the first thing any engineer will ask for.

Grid alarms: usually the grid, not your inverter

The inverter constantly measures the mains supply. If voltage or frequency moves outside the range it is set to accept, or the supply disappears, it disconnects. UK connection rules require this.

• NO-Grid: the inverter can’t see the mains supply. Expected in a power cut. If the house has power, check whether the solar breaker in your consumer unit has tripped.

• OV-G-V: grid voltage is above the inverter’s limit. Solis notes that occasional alarms recover on their own.

• UN-G-V: grid voltage is below the limit.

• OV-G-F and UN-G-F: grid frequency is above or below the limit.

• GRID-INTF: the inverter has detected interference or a distorted waveform on the grid.

If OV-G-V keeps appearing on sunny afternoons, the cause is often high local voltage rather than a faulty inverter. Solis says protection settings should only be changed with the network operator’s approval. In the UK the settings are fixed for compliance, so the answer is to report the voltage, not to change the limits. Our guide to inverters that shut down on sunny days explains how.

Insulation and leakage alarms: call an engineer

These are about the panels, cables and connectors rather than the grid.

• PV ISO-PRO: insulation between the solar wiring and earth has dropped too low. Solis notes it can appear in the early morning, late afternoon or in rain, when everything is damp.

• ILeak-PRO: leakage current to earth has gone above the inverter’s limit.

• ARC-FAULT: on models with arc detection, the inverter has detected a DC arc. Solis points to loose or damaged connectors and cracked panels as causes.

• OV-DC: the voltage from the panels is above the inverter’s maximum. This normally points to a design or configuration issue rather than something that appears out of nowhere.

One insulation alarm on a wet morning that clears as the day warms up isn’t unusual. Repeated alarms mean a fault somewhere in the DC wiring, and an arc fault always needs investigating. Solar panels produce DC voltage whenever there is daylight, so testing the array is work for an engineer with the right meters and protective equipment.

Temperature alarms: OV-TEM and UN-TEM

OV-TEM means the inverter’s internal temperature is too high. Solis’s advice is to check the installation: direct sunlight on the unit, poor ventilation, or the mounting position. An inverter in a hot loft or behind boxes in a cupboard will struggle in summer. UN-TEM is the opposite: the ambient temperature is too low. Both protect the inverter. If either happens often, ask your installer whether the location is right.

Hybrid systems: battery and meter alarms

On Solis energy storage inverters, a group of alarms covers the battery and the meter.

• CAN_Comm_FAIL: the inverter has lost communication with the battery.

• Alarm1-BMS and Alarm2-BMS: the battery’s own management system has raised an alarm. Solis suggests restarting the battery; if it persists, it needs an engineer and possibly the battery manufacturer.

• Failsafe: the inverter has lost contact with its meter. Without it, the system can’t see what the house is using or exporting.

• A battery not connected alarm (shown as a code on some models) means the inverter can’t see the battery at all.

Meter and battery communication alarms often explain a battery that won’t charge or won’t discharge. Our guides to a battery not charging and a battery not discharging cover the symptoms.

Internal alarms: the inverter itself

Alarms such as RelayChk-FAIL, DSP-B-FAULT, INI-FAULT, 12Power-FAULT, IGBT-OV-I and DCInj-FAULT relate to the inverter’s own electronics. For most of these, Solis suggests a restart and then contacting the manufacturer if the alarm doesn’t clear. A safe restart means switching things off and on in a set order, which differs between models and between grid-tied and hybrid systems. Don’t do it from memory or a forum post: ask your installer to talk you through it, or let an engineer do it.

An internal alarm that comes straight back after a restart usually means a repair or a replacement. Our page on inverter replacement explains the options, including for older systems on the Feed-in Tariff.

What you can safely check yourself

1. Is the alarm active now, or only in the history?

2. Note the exact message, the time and how often it appears.

3. Has there been a power cut, a storm or work on your electricity supply?

4. Check the solar breaker in the consumer unit. Reset it once if it has tripped; if it trips again, leave it off.

5. Make sure nothing is blocking airflow around the inverter.

6. Photograph the inverter label and the screen showing the alarm.

Don’t open the inverter, the battery or any isolator covers, unplug cables, or switch DC isolators on a guess. If you smell burning, see scorch marks or hear crackling, switch off at the consumer unit if you can reach it safely and call an engineer.

Who to call

Start with the company that installed your system. If they have stopped trading, our guide on what to do when your solar installer has gone bust explains your options. We install Solis equipment and inspect and repair Solis systems whoever fitted them, through our solar servicing team.

Frequently asked questions

My Solis inverter says NO-Grid but the house has power. What should I check?

Check the solar breaker in your consumer unit. If it has tripped, reset it once. If it trips again, or the breaker is on and the alarm stays, call an engineer.

Is PV ISO-PRO dangerous?

A single alarm on a damp morning that clears is common. Repeated or persistent alarms mean an insulation fault on the solar side that an engineer should find, because damaged DC cabling can be a fire risk.

Why does my Solis inverter show OV-G-V on sunny days?

Usually because the local grid voltage is high, and your inverter is disconnecting as it is required to. It is worth reporting to your network operator rather than changing settings.

Can I clear a Solis alarm from the app?

Many alarms clear on their own once the cause has gone. Clearing one that keeps returning without finding the cause only hides the problem.

Do you repair Solis inverters you didn’t install?

Yes. We service and repair Solis systems whoever fitted them, across London and up to around 50 miles out.

Book a solar system inspection. If a Solis alarm keeps coming back, we’ll find the cause and tell you whether it needs a setting check, a repair or a replacement.