Technical Tjet 120 overboosting problem

[Daiton]

So here's my issue,loss of boost no engine fault code. Engine fault lights up p0243,but full boost and back to normal. Sometimes I can clear the code go out for drive then immediate boost loss,drive for 10-15 mins full boost comes back with no engine light. Then if I switch engine off and start back up again drive abit with full boost fault light show ugly head again with full boost. Clear fault code and I'm back to square 1. Any help would be fab,kind regards