Pete have you managed to get the filter going?
If not can you post a few pictures of the pipe lay out and the filter with the black cover off so I can see the pump?
Also if the thing still isn't going right diconnect the filter from the tank and drain it off into a big bucket then take the pump off the top and check it is functioning properly either in a bucket in the garden or in a bucket in the bath but becareful as the unrestricted flow rate on the pump is about 1500 lph and it is a relatively high pressure as well and don't get your fingers anywhere near the impellor its not like fluval impellors where you can jam your finger in and stop them these things on eheims will mince your fingers.
This link maybe helpful its a link to all the manuals for eheim filters, the only place the problem can be providing the pipe work is sound is with the pump.
http://www.eheim.de/eheim/inhalte/in...n&list=afilter
This is the parts list for the eheim 2250
http://www.eheim.de/eheim/pdf/en/ers...classic_GB.pdf
This is also a useful starting point on the eheim site:
http://www.eheim.de/eheim/inhalte/index.jsp?id=24861
There are links so you can ask for help/advice as well.