How can I fix my aqualisa shower?

I have this shower for about 5 years and suddendly the pump seems to have packed up. Interestingly, it suddendly resumed and lasted, apparently as good as new for the duration of the shower, but never worked subsequently. I cannot see any thing that might stop the pump, othr than to report that there does not seem to be power ... I have checked the input using a multi meter (max 20 V setting (DC)). There is mains power going to the transformer .... I feel that the transformer could be the problem. Any ideas, please? Should it be the transformer, can a replacement transformer be purchased?
Frank