Sorry - unable to answer your question, just wanted to add that i have a similar problem.
I have an aqualisa aquastream, it is about 9 years old and no problems until recently. Firstly it just stopped working (water coming through but no pump). I got in the loft to check power to transformer ok - it was. A short time later I tried the shower and it was ok again. A week later and the pump has started coming on (no water coming through as not switched on), it will run for a few minutes, stop, then start again five mins later. I have had to go back in the loft and switch off the power to the transformer. (Yes, it would have been much easier to have the power switvh in the airing cupboard!).
Bob, December 2007