Tap water only in Glow worm space saver 38?

Hello,
I'm renting a flat and there is a Glow worm space saver 38 boiler. We don't want the heating to work, we just need warm water for taps. How can we do it? We had the boiler turned to a minimum level (the thinnest line), and the time control at 'off'. We decided to switch it off and see what happens. There was cold water only in the taps, and it seems to me that the flat became a bit colder as well. We think it was heating the house as well although it was 'off'. How does it work? The temperature in the flat is fine but cold water is annoying.
Thanks for any help!