Peter, Thanks for your reply

"Shorts would indicate that there is too much carbon in the pre-chambers and that the glow plugs are grounding there and burning out. "

Is this an easy fix - something we can do or is is something a specialist would need to do and would it be very costly?

Thanks again, Cendy

Sorry about this question. After posting I found some info in the search on this. Should have looked there first.
Thanks anyway.