CH Hot water cylinder connections. One weeps!!!!

5 Jul 2010
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United Kingdom
My Indirect hot water cylinder has a total of 4x connections.

1x Cold feed in
1x Hot outlet

1x CH coil in
1x CH coil out

The lower cold feed has a female thread into the tank. It then has a brass coloured male adaptor that screws into the tank, which then has a 22mm nut and olive on the outside to connect to the 22mm feed pipe.

I have a small weep coming from just underneath the adaptor.
Because of the insulation (and lack of space) I cannot see if the weep is originating from the adaptor to tank thread, or the nut/olive to adaptor.

I drained down the cylinder. Unscrewed the fitting. Wrapped the male thread in ptfe tape and screwed it back it in. I then wrapped the olive and rescrewed the 22mm pipe back on.

But it still weeps!!!!

Has anybody any suggestions?

I plan to drain it down again and redo it, but perhaps some of you may have some tips to ensure it becomes water tight!

Thanks in advance.
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Smear some sealant such as Jet Blue onto the threads of the male fitting, then wrap more ptfe tape in a clockwise direction looking at the thread ends. Then, another smear of sealant and screw the thing back in.
When you screw these fittings in they invariably dont point in the way that you want - hence the need for the tape, but screw it in as far as you can.
Treat the olive the same way - but if it is heavily distorted you may have to replace that short length of depends where the leak actually is.
John :)

Many thanks for the reply.

I will have a look and see if I can get some Jet Blue, and try again


Can you please clarify what you said above about using the sealant and ptfe tape?

Put sealant onto the male thread of the adaptor, then wrap ptfe tape over the top of the sealant, then smear sealant over the top of the ptfe tape?
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Its certainly the belt and braces approach but it does work for me.....the sealant helps the tape to stick - and the tape needs to be wound in such a way that it actually goes into the screwed boss, rather than be simply pushed out of the way. Another layer of sealant cant do any harm!
Gas PTFE is thicker than normal stuff, and tape such as Loctite 55 is good (the dispenser rolls flat tape into a cord, which is simple to wrap around threads).
There are many sealants called LSX is good (in a tube) but it sticks so well thats impossible to undo. I use Boss White, Blue Hylomar or Jet Blue - whatever is to hand, really.
Copper cylinders are fragile - and don't like their fittings to be overtightened as the copper stretches, so go easy on the tank....!
By the way - I'm not a plumber, but I have an engineering qualification - maybe others would like to comment?
Be lucky!
John :)
I believe the reason why you are not to mix sealants with ptfe is that PTFE is an oil based derivative and is broken down by the oils in the sealants etc- this said hundreds of plumbers, myself included, have smeared jet blue over ptfe on threaded joints for some years now without too many problems.

I've never been particularly happy with threaded joints onto cylinder circ's, am considering going back to hemp on these.

Tightening up is best done hand tightening when cylinder empty and tightening fuly when full as water pressure strengthens (?) sides of cylinder. There is certainly less give in them anyway

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