bosch dishwasher?

This question has been posted in several forms twice already but I cannot find any answers (last was December 09)
we have a bosch dishwasher and the waste pipe got blocked at the drains. it stopped at 42 minutes left and will not start again. we have reset and tried a quick wash and an eco washer, the time comes up as normal (30 or 93 minutes) but it starts cycle and finishes part way through - we have checked filters and and for blockages to pump and waste extract from machine appears clear - it leaves water as the final ejection of water does not occur - any ideas how to remedy - is this a mechanical (pump type fault or and electronic control fault preventing completion of the cycle irrespective of programme. Any help appreciated