Andy, I took your advice after searching for answers to my Potterton Suprima 50 boiler problems. A quick call to Pottern (08706 060 780) where a department has now been organised specifically to deal with these issues. Very friendly, an engineer is on his way out on Monday (28 May 2007). Cheers for the pointer!
For reference, all details about the boiler and many other things can be found here:
http://www.interpartspares.co.uk/documents/index.php
The above is very handy, you can find installation instructions, user manuals and spare part lists.
Take care
Darren Hunter, May 2007