How do I restart my controller ?

Check the batteries are in the right wayround

Check the battery terminal is not fouling on any of the plastic mpunding (had that once with a specific battery powered device when I used "standard" batteries that turned out to have a positive terminal slightly wider than normal)

FWIW there is an online copy fo the manual here:

http://w3.siemens.co.uk/buildingtechnologies/uk/en/building-automation/residential-controls/documentation/Documents/REV24_Operating_Instructions_en.pdf

XXX
July 2016