Fox ESS Grid Volt Fault
Grid Volt Fault, often shown as Error 26, means the mains voltage has drifted outside the range your Fox ESS is allowed to work within. In the UK that window is typically around 216V to 253V, with figures that vary by region. The inverter disconnects to comply with the grid code (G98/G99 in the UK), then reconnects on its own once voltage returns to normal, so no owner action is usually needed.
What usually causes it
- High grid voltage during strong export. On a sunny day your own solar export can lift the local voltage, and if it climbs past roughly 250V the inverter steps back.
- A weak or rural supply. Homes at the end of a long line often see voltage swing wider than properties near a substation.
- A network (DNO) issue. The voltage delivered to your street may sit too high or too low, which is the network operator's responsibility, not yours.
- Low voltage at peak demand, less common, where the supply sags below the permitted floor.
How to handle it safely
- Wait and watch. If the fault appears briefly and clears, that is the inverter doing its job. It reconnects automatically once voltage is back in range.
- Note when it happens. If it shows mostly around midday on bright days, your own export is likely lifting the voltage. If it happens at peak evening demand, the supply may be sagging instead.
- Check it is not just one bright spell. An occasional trip on a very sunny day is normal and needs no action.
- If voltage is persistently out of range, do not keep resetting the inverter. Report it to your DNO (the network operator) or your installer, who can log the voltage and ask the DNO to adjust the supply if needed.
Quick decision flowchart
Related Fox ESS codes
FAQ
Grid Volt Fault keeps appearing on sunny days, should I worry?
Usually no. On bright days your solar export can lift the local voltage, and the inverter steps back to stay within the grid code. If it clears each time, that is normal. If it trips repeatedly all day or the voltage stays high, report it to your installer or DNO so the supply can be checked.
Do I need to do anything to clear Error 26?
No action is usually needed. Once the mains voltage returns to the permitted range, your Fox ESS reconnects by itself within a minute or two. The one thing to avoid is repeatedly resetting the inverter when voltage is persistently out of range, since that is a supply issue to report rather than something to reset away.
Helpful guides
Sources
- Fox ESS H1/AC1 inverter user manual and FoxCloud alarm list (Grid Volt Fault / Error 26 = grid voltage outside the permitted range, inverter disconnects per grid code).
- Fox ESS installer guidance on G98/G99 grid connection and reporting persistent out-of-range voltage to the DNO.