On Sun, 01 Jul 2007 17:18:27 +0100, Andy Dingley
wrote:

Several people (including myself) have noticed a slight smell of gas
in my house,

Gas isn't meant to leak. If it is leaking, it's likely to be either
significant enough to be a risk of explosion, or else it's coming from
the exhaust of the boiler / gas fire not being vented properly. The
second of these can also have a risk of CO along with it, and low levels
of that can certainly give the symptoms you describe.

Thanks to all for the helpful replies. The gas smell I and my vistors
have commented on, always seems to be confined to very limited areas
within the house, as though a cloud of it is hanging in mid-air. But
if methane is lighter than air as exoplained in this thread, that
seems to make it unlikely that it's gas we are smelling. On some days
I smell it, some days I don't. It seems to make no difference whether
the central heating is turned on. The boiler doesn't get used much for
heating tap water either. If I close the door to the offending room,
and go back in there after 24 hours, the smell has not built up, and
may just as likely be completely absent.

I have ordered my own leak detector now, so I will be able to spend
some time trying to trace it next time I smell it.

Thanks again.

Mike D