Thanks again for the ideas
In the end despite using both boiling water as the infed water and warming all pipes and valves with a small blow torch I had to totally disassemble one valve. it had been corroded badly and the smallest amount of undissolved agar was reducing the flow rate too much. After a full refurbishment of that valve the repair was successful.
Certainly using boiling water and a small blow torch is the best/ most economical technique if anyone else has the same issue in the future. I recommend disconnecting the chamber heating element and fixing the position of the water reservoir float with the chamber inlet pipe open. Run the autoclave and it will pump water continously until it times out because the float hasn't moved. This procedure can repeated many times quite safely.
thanks again
harvey
