Updated
Inverter Showing A Fault Code Or A Red Light
The box on the wall is showing an error, a red light or a blank screen, and generation has stopped.
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What's happening?
The inverter is the part of a solar system that works hardest and dies first. It converts the array's direct current into mains alternating current, synchronises it with the grid, and it does that every daylight hour for years — which is why inverters are commonly replaced once during a system's life while the panels are still going. Fault codes split into three families and it is worth knowing which you are looking at. Grid faults, where the inverter has disconnected because mains voltage or frequency went outside its permitted window; these often clear themselves and recur, and repeated ones point at the supply rather than the inverter. Isolation or earth faults, where the inverter has detected leakage on the DC side; these are the ones to take seriously, because they usually mean water or damage in the array wiring. And internal faults, where the unit itself has failed. Every manufacturer numbers these differently, so the code plus the model is what an installer actually needs.
What usually causes it?
- Grid voltage or frequency drifting outside the inverter's permitted operating window
- An insulation or isolation fault on the DC side, usually water ingress at a connector or junction
- Overheating in an unventilated loft or a sun-facing wall position
- A failed internal component after years of daily cycling, common at around a decade of service
- Firmware or communication faults that stop reporting while generation continues
- A DC or AC isolator switched off and never switched back on after other work
- Rodent damage to DC cabling in a loft, showing up as an isolation fault
Is it dangerous?
An isolation or earth fault code is a genuine warning: it means the inverter has detected current leaking where it should not, and the DC side of a solar array is live whenever there is daylight and cannot simply be switched off at the fuse box. Do not open the inverter, do not disconnect DC plugs, and do not ignore a code that recurs. Grid fault codes are usually benign. Anything accompanied by a smell, a buzz that is new, or heat at the isolator should be isolated at the AC side and reported.
Can I fix it myself?
Write down the exact code and the inverter's make and model before doing anything, and photograph the screen — codes often clear and are then impossible to describe. Check both isolators are on, since these get switched off during other work and forgotten. Look up the code in the manufacturer's manual, which is usually the same document your installer left. A single reset via the AC isolator, off then on after a minute, is reasonable once. Repeating it on an isolation fault is not.
When should you call a solar installer?
Call an MCS certified solar installer for any isolation, earth or insulation fault, for any code that returns after a reset, for a blank inverter, and for grid faults that recur daily. If grid faults are frequent, the installer can log supply voltage and, where it really is the network, take that evidence to your distribution network operator.
What will the solar installer actually do?
- Read the fault log from the inverter rather than relying on the code on screen
- Carry out insulation resistance testing on the DC strings to locate leakage
- Inspect DC connectors, junctions and cable entries for water ingress and rodent damage
- Log grid voltage over several days where the inverter is disconnecting on grid limits
- Replace the inverter where it has failed, matching it to the array and re-registering the system
- Re-commission and re-test the installation, and confirm the network notification is still correct
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