Aquatronic 2+ won't turn on?

We have an aquatronic 2+ electric shower, came with the house so at least 6 years old. When it was turned off following use on the shower unit today it tripped the consumer unit off. Then pulled the power cord to off.
Mains all came back on OK, however if the power cord is pulled on, it re-trips the unit, suggesting the issue is between the power cord & the shower unit.
Any ideas what could be wrong - have looked in the power cord box & taken the front of the shower unit off, no obvious damage or issues.
If it comes to buying a new one, can we fit ourselves or are bathroom electrics now regulated?

All help appreciated.

D&J
October 2012