I have a small leak in my hot water cylinder, where the upper end of the
indirect coil emerges. This appears to have a 1" BSP male thread with a
fibre washer and thin backnut to seal it to the tank. The fibre washer
appears to have got *spread* - probably when it was first made - and there
has long been evidence of slight seapage. However, this has got worse since
I disturbed the surrounding pipework for an unrelated cause.
It's all very difficult to get at due to the integral foam jacket (a little
of which I have cut away) and the 1" to 22mm reducing fitting which is very
close to the backnut.
If at all possible I want to fix it without any dismantling - since this
would involve draining the tank - and I might even damage the coil in the
I have tried smearing various substances round it to seal - including
plumbers mait and boss white - but these all need to be applied to a *dry*
surface and won't stick properly to a wet one.
Can anyone suggest an alternative which I can use - which will cure and
stick to the surrounding metal in the presence of water - maybe even
*requiring* water to provoke a reaction of some kind?
You can get a two-part epoxy "putty" that's supposed to be for exactly this
situation. But I had no luck with two different brands I tried - it just
wouldn't stick to wet copper in spite of the claims on the packet.
Think a tube of Fernox LX might be what you want - it cures in the presence
of water and I have had success in stopping leaks around rad valves with
You may need to apply it a couple of times and use a "bandage" to stop the
leak pushing through whilst it's curing.
email me at
richard at olifant d-ot co do-t uk
I think it's very unlikely to be a failure of the seal -
cylinders seem prone to pinhole leaks, either from corrosion or
from overenthusiastic fitting folding the copper into a weak
spot. A weak spot can fail years after fitting, often after you
disturb the pipes - as you've seen. And a tiny leak can seal
itself with scale, which will drop off when you disturb the
Unless the cylinder is pretty new, I doubt you'll get away with
patching it except as a very temporary measure. It sounds like
time for a new cylinder. Sorry.
This has happened to me twice before. I've attempted repairs with
epoxy and Fernox LS-X. The method that came closest to working
was LS-X, wrapped with strips of LS-X-soaked cloth, reinforced
with twisted wire and cable ties to keep the cloth tight, more
LS-X, more cloth, more wire... This reduced the problem enough to
ignore it for a few days - long enough to buy and fit a new
Be aware that if you've made a pinhole leak worse by messing with
the pipework, there may be another one you haven't noticed yet...
Many thanks to all who replied with various ideas.
I seem to have fixed it without any fancy sealants. I managed to slacken the
backnut a bit and to remove the broken fibre washer - making the leak quite
a lot worse temporarily!. I then wound some ptfe tape round the thread
behind the backnut, followed by a smear of plumbers mait over the top. This
almost cured it, but I couldn't fully tighten the backnut because I didn't
have a thin enough spanner. I could partially tighten it by tightening the
1" to 22mm reducer - but only until this bottomed on its threads.
I then had the idea of *making* a thin spanner, and looked around for a
suitable piece of metal - and then remembered that I had a propane regulator
spanner in my caravan. This wasn't quite big enough, but by removing some
metal and putting a little bend in it, it did the job brilliantly. The
backnut is now tight - and the whole thing appears to be leak-free.
That's the pioneeering spirit.
The half decent plumber who did actually produce some half decent
plumbing has a car full of 'supplied washers' which he discards on every
new fitting, relying on silicone rubber, hermetite, ptfe tape, hemp and
None of his seals leak, and none of the ones I made copying his
techniques leak either..
You _will_ remember to buy a new one before you next go caravanning, won't
The most dangerous component in a car is the nut that holds the steering
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