Roger Mills wrote:
I have gate-type isolator valves either side of my circulating pump.
These have recently started leaking slightly - not from the gland
round the shaft, but from the point where the gate mechanism screws
into the body. They have fibre washers which seem to have perished.
Tightening helps a bit but there is still a slight drip . . drip.

I intend to replace the valves - probably with ball rather than gate
types (any comments?). This will, of course, require the system to
the partially drained - so I need to wait for a convenient time - and
need a short-term solution.

In a recent post concerning a leaking joint on a radiator valve,
someone suggested using a silicon sealant. However, all the tubes of
sealant which I have got state that the surfaces must be clean and
*dry*. There's no way I can make my surfaces dry - until I fix the
leak!

Does anyone have any suggestions of anything I can put on a damp
surface, which will still seal?

TIA,
Roger

Those small tubes of Fernox leak sealant might do it. It worked for me with
a leak on the outlet boss of a very large roof tank, still ok after 4 years.