The Aqualisa Digital shower installed about 5 years ago has always gone to boost mode following a power cut, (which is becoming more frequently these days). I find this problem frustrating and enquiries to Aqualisa unhelpful.

A recently installed similar shower to an ensuite doesn't have this problem, in that the boost turns off when the button is pressed.

On reflection, this product is not recommended by me.

Vaughan Saunders, June 2016

Turn off the power to the shower and leave it off for an hour. When you turn it on again you should be able to get it out of boost by pressing the boost button.
Turning it off for just a minute or two does not work. Perhaps it's because there may be residual current getting to the control box.

Roz, August 2022