We have been plagued by problems of minor (thankfully) leaks in our
airing cupboard which is a spaghetti of pipework around the how water
cylinder. The main culprit was the essex flange and this was replaced
and, despite needing tightening recently, is now watertight. The
exacerbating factor has also been that we were running the water much
too hot with the therrmostat on the element turned up full (80deg) -
lovely hot baths but lethal and I can't imagine it's done much for all
the joints etc.

Anyway we now find there is a slow but steady drip coming thru the
boards on which the tank sits but I cannot see the source of the leak
itself. I can see only four joints that could leak - the element, the
inlet, the main outlet and the essex shower outlet - all of these
appear to be sound and dry.

Is it possible that the tank itself (copper with that dry foam
insulation stuck all over it and about 20 years old I imagine) has some
kind split/hole in it?

Is there anything we could use like radweld (?) to seal it up? The
thought of having to replace the tank (meaning getting a plumber in to
do it) is a bit of a nightmare cost-wise!

Thnaks,
RB