These pumps are not really worth repairing I have seen them on Tapstore for as little as £136.00 http://www.tapstore.com/acatalog/New_Team_Varispeed_Si_Pump_1_50_Bar.html
I am a bit confused as to why the boiler Pressure dropping would cause this damage are you sure that it is fitted correctly. There is good info on the pump at http://www.new-team-pumps.co.uk/Newteam-Varispeed-si-Shower-Pumps.html
you can download the installation instructions on the website as well this might help.
Tim Clark
June 2008