Many thanks for replies and words of wisdom. I can't figure out how to quote another poster but I think I'll be patient and hang on for now.
I apologize again for not naming the manufacturer but I can't be certain the delay is down to them - something beyond their control could be holding things up and although I know the Amp was shipped, I do not know when it arrived at their factory!.
To be fair to the manufacturer, the dealer told me they wanted the Amp back because the fault I reported was completely unique, and was something they had never encountered before. He told me they wanted to examine the unit themselves in order to diagnose the exact cause of the fault. He also told me the distributor had said that faults with this manufacturers products were 'practically unheard of!' and that everyone associated with it was 'completely baffled.