Sit down. RTFM. Properly.
http://www.securetogether.com/files/7514/6916/4012/user_guide_H27XL-USeries21.pdf
Look at page 5
Each channel (Heating, Hot Water) cAN BE TORNED "off" permanently.
I quote:
OFF - Channel will be constantly ‘OFF’, there is the ability to turn off heating during summer without altering the programme times. 1 or 2 hour boost still available.
Just press the select button for the channel you are interested in.
1- Press SELECT once. Programme goes from AUTO to ALL DAY
2 - Press SELECT again. Programme goes from ALL DAY to
ON
3 - Press SELECT again. Programme goes from ON to OFF
XXX
September 2016