My Fronius inverter isn’t working: what to check step by step (307, 509, 522, no grid)

A Fronius inverter that is hardly ever producing power is likely to be faulty. In most cases, the problem lies with the solar array, an open-circuit protection device or the mains supply. Follow this sequence of checks and you’ll be able to resolve most issues without having to dismantle anything.

1. What does the investor say?

Before you do anything, check the display (Primo/Symo) or the web interface and Solar.web (GEN24). There are three possible scenarios:

Screen off and LEDs off: There is no DC or AC voltage. Proceed to step 2.
Screen lit with status code: look for the code in the Fronius code guide. The most common ones are 307, 509, 522/523 and those in the 100 series.
Screen on, no code and 0 W: Normally, the inverter is waiting for the DC voltage to exceed the minimum start-up voltage, or the smart meter has a feed-in limit of 0 W and there is no consumption in the house (see Smart Meter).

2. Protective devices: DC isolator, fuses and AC circuit breakers

The DC isolator The circuit breaker must be set to ON. Following a storm, it is common to find it switched off by the SPD or by the installer themselves.
Check out the string fuses in the DC panel (if any) and the surge protector: An SPD with the indicator in the red must be replaced.
The AC circuit breaker The inverter must be connected and, in three-phase Symo systems, all three phases and the neutral must be connected (code 448 if N is missing).

3. Solar field voltage

The Fronius requires a minimum DC voltage to start up: approximately 80 V on Primo/Symo and a few 65 V at GEN24. With the system switched off, and only if you have electrical training, measure the open-circuit voltage (Voc) of each string at the DC terminals:

0 V: Open circuit. Loose MC4 connector, blown fuse, broken cable or a panel with a damaged diode/junction box.
Very low voltage compared to the other string: There is one or more panels that are short-circuited or in the shade. This corresponds to code 522/523.
Voltage is correct but it won’t start: reversed polarity (rare, but it can happen after a repair) or an internal fault.

A quick tip: in Solar.web, compare the MPPT1 and MPPT2 curves. If one string is flat whilst the other is producing power, the fault lies with that string, not the inverter.

4. Electricity grid

Codes 102–108: the grid is out of range. The inverter will only reconnect once the voltage has stabilised. If this occurs daily, measure the voltage at the connection point: if it exceeds 253 V, the inverter will shut down in accordance with regulations.
Code 567: the inverter reduces output because the mains voltage rises when feeding into the grid. This is usually due to a long or undersized AC cable between the inverter and the distribution board.
Also check the country code / network standard configured. An inverter configured for another country may not be compatible with the Spanish grid.

5. Code 509: no injection in the last 24 hours

This is a warning, not a fault: the inverter has not been generating power for a full day. This message appears following an open isolator, snow or a prolonged power cut. If the solar array and the grid are both working properly, restart the inverter.

6. Full reset

1. Switch off the AC circuit breaker.
2. Open the DC isolator.
3. Wait 5 minutes until all the LEDs have gone out.
4. Close the DC isolator and wait for the display to start up.
5. Switch on the AC circuit breaker. The inverter takes between 1 and 3 minutes to synchronise with the grid.

7. If it still isn’t producing

At this stage, the remaining causes are hardware-related: power stage, mains relay (457), current sensor (315/474) or persistent insulation fault (502). As an authorised Fronius service centre, we can check the inverter’s service history on Solar.web and process the warranty claim or repair.

FV Componentes is Fronius authorised technical service centre (Fronius System Partner). If the problem persists after carrying out these checks, please open a ticket at Technical support with the serial number and a screenshot of Solar.web, and we’ll diagnose it.