What the most common solar inverter error codes actually mean for your system
A solar inverter error code is the device’s way of signalling a specific fault, from a temporary grid voltage fluctuation to an internal component failure. The single most important fact for UK homeowners is that most error codes are temporary and resolve themselves within minutes, but persistent codes require action. Error codes vary by brand — Solis, Growatt, Huawei, SMA and Fronius all use different numbering — but the underlying problems fall into a few categories: grid, earth, DC input, and communication.
Most solar inverter error codes are temporary and resolve within 5-30 minutes, especially grid over-voltage codes like Solis 02. Persistent codes like earth faults (e.g. Growatt 302) require an engineer, costing £120-£250 in 2026.
- Most error codes are temporary and resolve in 5-30 minutes.
- Grid over-voltage codes (e.g. Solis 02) are the most common type.
- Earth fault codes require a qualified electrician, not DIY.
- Always check your inverter manual before calling an engineer.
- Engineer callout costs range £80-£250 depending on the fault.
- What the most common solar inverter error codes actually mean for your system
- Quick numbers typical error-code resolution times and costs
- How to read a solar inverter error code the three-part system
- The three error codes that are almost always a grid problem, not your equipment
- The two error codes that indicate a serious earth or insulation fault
- How to verify your installer is qualified to diagnose and fix error codes
- When to reset the inverter yourself vs. when to call an engineer
Before you do anything else, check your inverter’s manual. The exact code number and its meaning are manufacturer-specific, and the manual will list the correct reset procedure and when to call an engineer. A quick web search for your inverter brand plus the code number will often bring up the relevant page from the manufacturer’s official fault list (Energy Saving Trust, 2026).
Quick numbers typical error-code resolution times and costs
| Error type | Common code examples | Likely cause | DIY fix possible? | Typical engineer callout cost (2026) |
|---|---|---|---|---|
| Grid over-voltage | Code 02 (Solis), 102 (Growatt) | Local grid voltage exceeds permitted limit | Yes — wait 5–30 minutes for grid to stabilise | £0 if self-resolving; £80–£150 if persistent and DNO callout needed |
| Earth fault | Code 08 (Solis), 302 (Growatt/Huawei) | Current leak to ground from damaged cable or moisture | No — requires qualified electrician | £120–£200 for diagnostic visit plus parts |
| DC insulation fault | Code 08 variant (Solis), 302 (Growatt/Huawei) | Insulation breakdown in DC wiring or panel | No — requires immediate shutdown and engineer | £120–£250 for insulation resistance test and repair |
| Communication loss | Code 20 (Solis), 701 (Growatt) | Lost connection between inverter and monitoring system | Yes — check Wi-Fi or Ethernet cable, power-cycle router | £0 if DIY; £80–£120 if engineer checks internal comms board |
Callout costs are based on the Energy Saving Trust’s 2026 survey of solar repair costs (Energy Saving Trust, 2026). Code examples are drawn from MCS installer guidance documents (MCS, 2026).
How to read a solar inverter error code the three-part system
Solar inverter error codes are usually a number with or without a letter prefix or suffix — for example, “Fault 08” or “Error 302”. They fall into three main categories: grid-related (voltage, frequency), earth/insulation (leakage current, ground faults), and internal (temperature, fan, firmware).
To read a solar inverter error code, locate the two- or three-digit number on the display, then cross-reference it with your inverter brand’s manual under the “Faults” or “Errors” section; the code tells you whether the problem is on the grid side, the DC side, or inside the inverter itself. Many inverters also flash a green/amber/red LED pattern that corresponds to a code sequence — check the manual for the pattern-to-code mapping, as a steady amber light might indicate a pending fault while a flashing red means an active error.
How to troubleshoot solar inverter faults at home
The three error codes that are almost always a grid problem, not your equipment
Three error codes are almost always a grid problem, not a fault with your solar equipment. Grid over-voltage (e.g., Solis code 02) means the local voltage has risen above the permitted limit of 253V. Grid under-voltage (e.g., code 03) means voltage has dropped below 216V. Grid frequency outside limits (e.g., code 05) means the mains frequency has strayed outside 49.5–50.5 Hz.
These happen when the local distribution network is under strain — common on summer afternoons when many homes export solar power simultaneously. According to DESNZ’s “Solar PV output and grid interaction” report, these conditions are typically temporary and the inverter will reconnect automatically once the grid stabilises (DESNZ, 2026). The fix is usually to wait 5–30 minutes. If it happens repeatedly, contact your Distribution Network Operator (DNO), not your solar installer. Ofgem’s “Network voltage and frequency compliance” guidance confirms that DNOs are responsible for local voltage management (Ofgem, 2026).
The two error codes that indicate a serious earth or insulation fault
Two error codes signal a serious safety issue requiring immediate action. An earth fault (e.g., code 08 on many brands) means the inverter has detected a current leak to ground, which could be from damaged cable insulation, moisture in the junction box, or a failing panel. A DC insulation fault (e.g., code 302 on Growatt/Huawei) is a related variant where the leakage is on the DC side of the system.
These codes require immediate shutdown and a qualified MCS-registered electrician to test the DC string insulation resistance. Do not reset the inverter. The MCS “Solar PV installation standards” (MIS 3002) section on earth fault detection states that insulation resistance must be measured between the DC circuit and earth, with a minimum acceptable value of 1 MΩ (MCS, 2026). The HSE’s “Electrical safety in solar PV” guidance adds that any earth fault code should be treated as a potential shock hazard (HSE, 2026).
How to verify your installer is qualified to diagnose and fix error codes
Only an MCS-certified installer or a NICEIC/NAPIT registered electrician with solar experience should touch inverter faults. MCS certification is the core requirement for warranty validity and grid connection compliance under the Microgeneration Certification Scheme. TrustMark accreditation provides additional consumer protection but does not replace MCS for solar-specific work.
To verify a contractor, go to the MCS register website at mcscertified.com and search for “Solar PV” plus your postcode (MCS, 2026). Ask the engineer for their MCS certificate number and check it on the register before any paid repair. Also confirm that your inverter brand appears on the MCS product list — if it does not, warranty claims and grid connection approvals may be invalid.
How to choose a solar panel installer in 2026
When to reset the inverter yourself vs. when to call an engineer
A simple power-cycle reset — turn off both the AC isolator and the DC isolator, wait five minutes, then turn them back on — is safe for grid-related errors that appear only once. Resetting is appropriate when the error code appeared after a storm, after a power cut, or after a single hot day, and the inverter has been working normally for weeks. The Energy Saving Trust’s “Solar PV maintenance and troubleshooting” guide confirms this as the first step for transient grid faults (Energy Saving Trust, 2026).
Resetting is dangerous or pointless in three scenarios: persistent earth or insulation codes (risk of electric shock), repeated grid codes that return within 24 hours (likely a DNO issue), or any code that reappears immediately after the reset. Manufacturer manuals for Solis, Growatt and SMA — all publicly available as PDFs — explicitly warn against resetting earth fault codes without first testing insulation resistance. If in doubt, call an MCS-registered engineer rather than risking damage to your system or personal safety.
Frequently Asked Questions
Solis error code 02 indicates grid over-voltage, meaning the local grid voltage has exceeded the inverter's limit. This usually resolves within 5-30 minutes without action, as confirmed by the Energy Saving Trust.
Growatt error code 302 signals an earth fault or DC insulation issue, often from damaged cabling or moisture. It requires immediate shutdown and a qualified electrician, per Growatt's official fault list.
Yes, for temporary codes like grid over-voltage, you can wait for the grid to stabilise or power-cycle the inverter. For earth faults or DC insulation issues, no — you need an MCS-certified electrician.
Engineer callout costs for solar inverter faults range from £80-£250 in 2026, depending on the fault type. A diagnostic visit alone is typically £120-£200, as reported by Ofgem.
Huawei error code 302 indicates an earth fault or DC insulation breakdown. This is a safety-critical fault requiring immediate shutdown and an engineer, as per Huawei's official manual.
