Your inverter is the brain of your solar system — it converts the DC your panels produce into the AC your home uses, and it is the component most likely to fault. When it does, the panels keep generating but nothing reaches your home. The good news: most fault codes tell you exactly what is wrong. This guide translates the common ones into plain English, and tells you honestly whether the fix is a reset, a repair, or an upgrade.
First: what the warning light means
Most UK inverters use a simple traffic-light scheme. Green (solid or pulsing) is normal generation. Orange/amber is usually a warning or standby — often a grid issue the inverter is waiting out. Red (solid or flashing) is a fault the inverter cannot clear on its own. Before anything else, note the exact code on the display or in the app — that code is the key to everything below.
The three fault families
Almost every inverter fault falls into one of three groups:
- Grid faults — voltage or frequency outside the permitted G98/G99 range. Common on rural or end-of-line connections. Often self-clears; if it recurs daily, the grid connection or settings need attention.
- Isolation / insulation faults — the inverter detects current leaking to earth, usually from water ingress in a connector, a damaged DC cable, or a degrading panel. This is a genuine safety stop and should not be repeatedly reset.
- Internal hardware faults — failed cooling fan, swollen capacitor, or a failed power stage. These are the end-of-life faults, and the point at which repair-versus-upgrade really matters.
Common codes by brand
- SMA (Sunny Boy): codes in the 3xx range are grid faults; 7xx are internal; "Riso" / event 3501 is an insulation fault. A single grid code often clears; a recurring Riso fault means moisture or panel degradation.
- Solis: "OV-G-V" / "Grid OV" is grid over-voltage (very common in the UK); "DC-INTF" and "DSP-FAULT" are internal. Persistent over-voltage may need a G99 settings review rather than a new inverter.
- Fronius: "State 522/567" are grid related; "State 105–109" point to internal power-stage issues. Fronius units past 10 years often fail on the fan or relay.
- SolarEdge: "Error 18xx" are isolation/arc faults (safety — do not ignore); optimiser comms errors point to a single panel or optimiser, not the whole system.
- GivEnergy: battery-comms and BMS warnings are usually a firmware or connection issue, not a dead unit; an inverter over-temperature warning points to ventilation.
- Enphase: because each panel has its own micro-inverter, a fault is usually isolated to one or two panels — the rest keep producing. Per-unit replacement is straightforward.
Reset, repair, or upgrade — the honest decision
Reset if the code is a one-off grid or comms event: AC isolator off, DC isolator off, wait five minutes, power back on (DC first). If the same code returns within 24 hours, stop resetting — you are masking a real fault.
Repair / like-for-like swap (£800–£1,500 fitted) makes sense when the system is under roughly 8 years old and the panels are healthy. See our solar inverter replacement cost guide for the full breakdown.
Upgrade is usually the better-value route once the inverter is 10–12 years old, because that is its design lifespan and the rest of the system is ageing too. For the same outlay as a like-for-like swap you can fit a hybrid inverter that makes your system battery-ready — and a battery retrofit lifts self-consumption from around 30% to 80%+, which a new inverter alone cannot do. This is exactly the situation our solar panel maintenance and upgrade service is built around: we diagnose honestly, then quote both the repair and the upgrade so you can choose.
What we do
Our free diagnostic reads the fault code, checks the inverter, panels, strings and isolators, and tells you whether you need a reset, a part, or an upgrade — for any brand, whether or not we installed the system. If a quick fix is all you need, we will say so. If it is end-of-life, we will design the upgrade that pays back fastest. Book a free solar system health check or call 0800 099 6606.