I (unfortunately) have a problem when it comes to simply wanting hot water - the system doesnt work without the radiators... so I have to turn them off, but this year, despite the nozzles being turned off, 2 of the radiators still come on!!!!!!
Fortunately it only takes 20 mins for my water to heat up enough for my days requirements.
However last night I turned it on.... then went to the pub.... when I got back it was absolutely sweltering - spent the night with the bedroom window open.
So.... short answer to your question... yes I had the heating on....
but didnt mean to!!!!!! lol ;-)