Thanks Johandup
The inverter is powered by solar (15 x 275w 3S/5P) and a GCL 5.6kwh lithium. The unit actually starts and runs the pump but with a flashing fault light which I think is overload warning. I installed the system for a client who bought it himself. I did warn him that the unit does not have the overload capacity to supply the inrush current which I can measure....82 Amps at 230 Vac. The unit rating is 5kw/5kVa which does not make sense to me. 5kVa at a power factor of .7 (which is probably optimistic) is 3.5kw.
I need a suitably sized unit that can take the punishment....I am investigating the Microcare 8Kw unit, I think that will be OK but I certainly do appreciate any input from people like yourself.