Fox ESS Grid Lost Fault
Grid Lost Fault means your Fox ESS cannot detect the utility grid, so it stops exporting and waits. The mains supply to the inverter is absent or disconnected. Almost always this is a tripped breaker or an AC isolator left off, not a fault in the inverter, and it clears on its own once grid power is back.
What usually causes it
- The AC isolator under the inverter is off. The small rotary switch below the unit may have been switched off.
- A tripped breaker. An MCB or RCBO for the solar circuit at the consumer unit has tripped.
- A genuine grid outage or planned power cut in your area.
- A loose AC connection, less common, that an installer needs to check.
How to handle it safely
- Check the AC isolator. The switch directly under the inverter should be ON. If it is off, switch it back on.
- Check the breaker. At your consumer unit, see whether the solar MCB or RCBO has tripped. Reset it once if it has.
- Check for a wider outage. If your lights are off too, it is a grid power cut. The inverter reconnects automatically when power returns.
- If a breaker keeps tripping or feels weak, do not keep forcing it. Fox ESS specifies a bi-directional 100mA RCD/RCBO, not a 30mA type, so have your installer confirm the right device is fitted.
Quick decision flowchart
Grid Lost Fault appears
↓ check the AC isolator and breaker
✅ Isolator or breaker was off → switch on, the inverter reconnects on its own.
❌ Breaker keeps tripping → stop resetting, have the AC side and RCD checked.
↓
If grid power is present and the fault stays, contact your installer.
Related Fox ESS codes
FAQ
Grid Lost Fault appears every evening, is that normal?
It can be. If it shows briefly around dusk or during known local power dips and clears itself, that is the inverter doing its job. If it appears at the same time daily and stays, ask your installer to check the AC connection and the breaker.
Do I need to do anything to clear it?
Usually no. Once the AC isolator and breaker are on and grid power is present, the Fox ESS reconnects by itself within a minute or two. You only need to act if a breaker has tripped or keeps tripping.
Helpful guides
Sources
- Fox ESS H1/AC1 inverter user manual and FoxCloud alarm list (Grid Lost = no utility grid detected; check AC isolation and protective device).
- Fox ESS installer guidance on grid connection and the required bi-directional 100mA RCD/RCBO.
⚠️ Safety disclaimer. Solar inverters carry lethal DC and AC voltage even when "off". This guide covers checking the AC isolator and breaker only. Any AC wiring, RCD or internal work must be done by a licensed installer or electrician.