In uk.d-i-y, Skirrow wrote:

With the days getting colder I have started using an electric heater
in my garage. The only problem is that it has a very short power lead
so I have plugged it into a 2way extension which is plugged into a
double socket in my garage which in turn runs to a fuse box in the
garage and then into the house (into an old cooker outlet).

Anyway, the other day, after being in the garage with the heater on
for a couple of hours, I unlugged it and noticed that the plug was
warm, rather foolishly I stuck my finger on the prongs and the live
one was bloody hot.

Not at all foolish: the plug wasn't live, after all, and you've found
something which needs attention.

Can anyone tell me whats causing this and what I can do to fix it as
I'm a bit scared of melting the socket or burning the garage down.

The heater is a fairly significant load (2kW typically, maybe 3kW).
You may well have a loose connection in the extension socket or in
the heater plug. Open both up (if you need telling to unplug the
extension lead first, don't read on or do any of this stuff!!) and
see which it is; you may need to cut back to fresh cable if the
insulation's got charred.

It could also be that the 2-way extension socket is simply cheapo
junk which makes poor contact with the plug pins - many trailing
sockets are fine for light loads like, well, lights, drills, computers
and so on, but don't make the best of contact and will heat up when
used on a heavy load. A better form of trailing socket from that
point of view is a metalclad socket, with a cable gland used to
provide proper strain relief. Being finicky, they're not really meant
to be bashed about on their own - it's possible one of the round
blanking discs could fall out if subjected to rough handling, exposing
the innards to a careless finger. Mounting it on a bit of scrap wood a
little larger than the socket would improve its robustness.

HTH - Stefek