Pablo wrote:
At the moment I only have my hot water on in the house (twice a day via
the timer). I have noticed that the small expansion tank in the loft
(as opposed to the big tank) has hot, brown water in it.
Is it normal for there to be hot water in this tank? Any comments would
be appreciated. Thanks

Oh dear. It sounds as if it's pumping over. The brown is rust
from the insides of iron on your CH system (radiators, boiler,
etc.). It's possible, if everything else is OK, that the pump
is set too fast. Get your central heating going, and see what
comes out of the pipe leading into the top of the tank, the
one that just ends in mid-air. Turn the pump down, if possible,
and see whether that stops any water coming into the tank from
the vent pipe referred to, and check that the rads. still get
hot. The system may need draining/flushing, and an inhibitor
would be a good idea.