any advice?

According to instructions you must use same make of batteries and do not use re-chargeable batteries.
If you have inserted new batteries then you have a faulty unit draining the batteries.

If no manual you can download a pdf file www.mirashowers.co.uk

Note! When batteries are replaced, control unit activates “Clock Setting” mode. Reset the time and press “ ”. you probably know this already but just added it.

bob
September 2013