You haven't given us much information so I can't give you much of an answer. What model generator? By 'fine' do you mean it generates 110V correctly or just that nothing trips? What is tripping - an MCB? Does 'no load' mean no plugs in the sockets?
If I guess that it is a type with a 110V outlet, a 230V outlet and a selector switch, and it does generate 110V OK, then likely causes are:
a) short in wiring to 230V socket
b) faulty selector switch not breaking parallel connection of windings before making series
c) short in generator windings bridging ends that are paralleled in 110 mode but 110V or 230V apart in 230 mode.
a) and b) probably commercially viable repair, c) maybe not.
But first, fill in the blanks...
