There are no connections to the unit except for the battery, which is healthy. Looking at other similar questions here, the answer seems to be to contact the supplier. We cannot do that. If the unit is faulty, what options are there for repair? The unit was installed in 2016.
Start with making sure the internals of the inverter are ok. No dust no moisture wildlife etc.
Remove all AC wiring and try they it again making sure the battery is ok.before this.
Step one and two are completed by you already.
If it is still not ok, then you can still take it in for repair. While you are not under warranty they can still be repaired. The centre for repairs near you would be able to be more specific
