Warning What does this mean?

Your system is down or running degraded, but this is not an immediate safety danger. Work through the safe steps below.

Fronius Inverter STATE 309 Error: Meaning, Causes & Safe Fix

STATE 309 means the DC input voltage on MPPT 1 is too high — the solar string voltage exceeds what the inverter allows. The inverter returns to its startup phase.

What should I do first?

Two quick questions — we'll point you to the right starting point.

Is this code still showing on your inverter's display?

What this code means

Each MPPT input has a maximum DC voltage (up to 1000V depending on model). STATE 309 appears when the string connected to MPPT 1 exceeds that limit — most often on cold, bright mornings when panel voltage peaks, or if the string was designed with too many panels. The inverter returns to its startup routine instead of feeding power.

What is this downtime costing you?

Rough estimate while your system isn't producing. Adjust the numbers to match your setup.

System size (kW) Peak sun hours / day Electricity rate ($/kWh)

–per day

–per week

–per 30 days

≈ – kWh of lost production per day.

Estimate only — assumes ~80% real-world output vs. nameplate. Actual losses depend on weather, shading, panel direction, and your tariff.

Common causes

A string designed with too many panels in series, so voltage peaks too high in cold weather
Very cold, bright conditions pushing panel open-circuit voltage above the limit
Incorrect string configuration after panel work
An MPPT settings mismatch

Safe steps to try

Work top to bottom, ticking off each step as you complete it. 0 of 5 done.

Note when it happens — cold mornings point to string design
Do not disconnect or rewire any DC strings yourself
Check whether it clears as the day warms up
Record how often it occurs
Contact your installer — string voltage issues need professional redesign

Is your inverter still under warranty?

Before paying for a repair, check — your installer may fix this free.

Brand Year installed

Based on typical standard warranty terms — always confirm with your warranty card or installer paperwork, as terms vary by model, region, and purchase date.

When to call an electrician

If STATE 309 persists, contact a Fronius-trained service technician (the official remedy). String overvoltage is a design and wiring issue — only your installer can safely reconfigure strings.

Frequently asked questions

Why does 309 appear on cold mornings?

Solar panel voltage rises as temperature drops. A string that is fine in summer can exceed the inverter's limit on a cold, sunny morning.

Can I just remove a panel from the string?

Absolutely not — DC wiring work must be done by qualified professionals with the system safely isolated.

Will 309 damage my inverter?

The inverter protects itself by not operating. But repeated overvoltage events are not good for it — get the string design checked.

Need a professional?

This fault may need professional diagnosis. Contact a qualified solar electrician in your area.

Sources: meaning and troubleshooting verified against the manufacturer's documentation — Fronius Operating Instructions (Symo/Primo) — 'Status codes and remedy' / 'STATE CODES' tables (Fronius docs 42,0410,0192 & 42,0410,1909 series)