 You don't need to be an 'investor' to invest in Singletrack: 6 days left: 95% of target - Find out more
Had a plumber in who has confirmed there are no leaks in the system so smell not coming from boiler/shower/rads etc but when hot water or heating on there is a strange slightly sulphury smell in this one bedroom. Smell always mid air and not always in the same place. it's driving us nuts.
only idea i have is that hot water pipes heating floor board which may be a bit rotten but its all carpeted so can't see anything. Wouldn't we smell any rot all the time though?
A conundrum.
Do you have auto bleeding valves on the rads?
Smells tend to be hightened in warmer tempretures. Check for a body under the floor boards. While your doing it you can replace your rotten boards.
once at my old house we had an awful smell for about a week ( it made you gip) it came from under the floor boards-i guess something died under there...i nver did look ! beware of the silver moon ! 
Time to call in the Ghostbusters ??
I had a strange smell in my bedroom a couple of weeks back. Eventually traced it to a dead sparrow that had got stuck in my bed drawer. F*ck knows how it got in there, was only a tiny gap. Little b*stard had shat everywhere as well.
Cue jokes from mates "the last bird that ended up in his bed died shortly afterwards"
Dust on a light fitting being burnt off?
try changing the sheets you dirty beggar!!
Time to call in the Ghostbusters
Theres a (old) man coughing in the back living room. A bit wierd but as long as he doesn't do it when I'm asleep then Im happy.
Have you been decorating in the last few months? We had the "rare" Crown paint problem:
http://www.bbc.co.uk/blogs/watchdog/2010/05/crown_paints.html
We'd replaced the carpet, the bed, curtains before we heard about this.
Dust on a light fitting being burnt off?
We had a similar thing years ago- but it was the light fitting itself started to smell when it heated up. Drove us mad for ages.