Hi all,
Yes lock the boiler up!, I have done this; it works!
One summer a few years ago I got a gas bill of £140 A MONTH!, because someone was leaving the heating on to dry their clothes, even though it was 80degs outside; I was rather mad!
As for electric it is tricky, I find lots of tenants (in an HMO) have game console, large tv's, stereo's, PC's etc. all on all the time and (of course) as they don't pay the bills leave the lights on.
They never learn or care so I just increase their rent every 6 or 12 months, using increasing energy bills as the excuse. It's usually only £10 per person (so maybe an extra 50 quid per house) but that helps.
But, by including bills in a fixed rent, I do tend to get more calls when a room is vacant. Quite simply they use the electric & gas not me, so they will pay.
Quite often the housemates "blame" one individual for constant electric wastage. So I increase his/her rent more - then they leave. Usually the bills then do drop as you've got rid of the "non-green" tenant! :-)))
Cheers