Can I turn it off?

Darned site truncated my reply so you didn't get the full story. Just read age 5 of the manual I linked to. Read slowly.

XXX
September 2016

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