Aquatronic power shower cuts out when being used?

The aquatronic power mixer was already installed in this house when I bought it. I believe it is a Mira one repackaged by Wickes.
The problem I have is that occasionally the shower will just stop while in use and then after a short while will restart again, this can happen several times during one shower. Can anyone advise as to why this happens please ? Is it a safety precaution because of water temperature ?

valerie
September 2017