Replacement hot water cylinder leak.

[Nick]

I have replaced an existing hot water cylinder. I reused the old compression joint at the bottom. It is now leaking, ever so slightly. I think it is a copper bent tap connector. Something like but for 28mm. i.e there is no olive.

The leak is very slight, I stuff a piece of toilet paper around the joint and overnight about half the toilet paper gets dampish the other half remaining dry.

I used a bit of Fernox LS-X fitting the joint, I was unsure how it was supposed to work. maybe it had a washer which had disappeared in 30 years?

Will the leak seal of its own accord, due to hard water?

If I do need to redo the joint, how are they supposed to work. i.e. what am I supposed to put in the joint. I used up all the LS-X but have an unopened tin of Fernox White Hawk.

Or I could take the bent tap connector off and solder a standard elbow and short pipe into a new standard compression fitting with an olive but would like to avoid extra work.

If its not obvious I know very little about plumbing, so simple answers please.

[Michael Chare]

PTF tape and Boss White can help, but are your sure you are using the correct fitting.

[simon mitchelmore]

If its got a shoulder which looks like it mates with the flat end of anothe r fitting (i.e. like a tap connector) then it needs a fibre or similar wash er to sit on the shoulder ring. If you haven't got said washer try about 8 laps of PTFE sealing tape just above the shoulder then tighten it up so it seals to the mating surface on other fitting.

Much better to fix it properly IME as an external leak sealer may fail at t he worst moment whereas once a fitting is tight its sorted period.

[Roger Hayter]

If it's a tap connector it should have a fibre washer. They are very common and standard, either 1/2" or 3/4". Tap connector washer should define it adequately. Most likely the latter size in this context. I've never seen a 1" one. The specified size is based on the nominal size of BSP threads, which in turn is based on the internal diameter of the pipe the threads would be traditionally be cut on; so if the spigot end of your tap connector (the end with the nut on) is about 22mm then this is a 3/4" one. A 1" one would be definitely more than 25mm.

[harry]

No. It's one of these.

Clean up the mating conical faces with wire wool and wrap some PTFE tape round so that the face is covered. It'll probably fix it.

[Nick]

Yes, indeedy, that is what it is, thank you. I spent ages looking for a match.

I had already done the wire wool. How many turns of PTFE? I'm not always successful with PFTE might a jointing compound not be easier for a novice such as myself?

[Tim+]

Hmm. Looks like the pipe is sort of crimped to make a fixed olive. Can't see that being great for sealing, or rather re-sealing if it's been wellies up too tight in the past.

It could. I've know small weeps to self-seal. The other suggestions of sealant might be worth trying but best of all would be a new fitting with an olive.

Tim

[harry]

There are no olives in cylinder connectors.

[harry]

PTFE tape comes in various thickness, so can't really say. Five or six layers plus maybe a dose of liquid PTFE??? You might have to bugger around a bit but normally this sort of thing can be fixed. Wind the tape on in tahe same direction as the nut turns to tighten. This avoids displacing the tape as you tighten up.

[DerbyBorn]

y say.

The nut is only applying clamping force - it is not helping to seal.

[Roger Hayter]

That looks like a good idea! Is it just hot water cylinders that fit them? Ordinary tank connectors don't seem to have the relevant taper?

[newshound]

I think it might well self-seal too, at that leak rate. While all the other advice is good, if the access is awkward I would personally try leaving it with a little catch-tray underneath for a few days.

[harry]

All pipe connection fall into one of two categories.

Conical faces that can stand slight misalignment. Tightening up pulls the parts into alignment. In this case it works because the thin metal of the tank can bend slightly. Needs heavy pressure/tightening to make a seal. Compression fittings fall into this category too.

Flat faces that require a gasket. Allows slight movement after tightening without leaks. Due to resiience of the gasket. Joint can be undone and remade (with new gasket?) As you have found, this may not be true of conical/taper joints.

Tank connectors work at very low pressures. They are used so that a hole can be drilled anywhere in a tank and the connector fitted. Your hot water cylinder has premade connection points because there is no access to the inside of the tank. (To fit a nut) And the water pressure is higher.

[Brian Gaff]

Is the joint under stress when the tank is full of water. My experience suggests that this flexing is not good fro compression joints at all. Brian

[Nick]

Not really. The pipe comes down from the loft and would easily move up and down about 2 or 3 cm. I'm not sure if it was the exact resting height but I didn't have to force it at all. I suppose I could put in pipe clips to clamp it against the wall, to remove any stress from the pipe's own weight.

The boiler feeds to the coil, 22mm cylinder connectors, did have more stress, one was too much and I redid the pipe work, the other sealed so I didn't worry about it.

Redoing the pipework I used trigonometry to calculate the pipe lengths exactly but even then it was very sensitive to angles whilst soldering. I wonder how plumbers do it. Maybe they are good at it or maybe they bend the pipes after soldering?

The top of the boiler hot water feed had a similar bent cylinder connector pipe to the cold water feed but the cylinder height was 5-10mm shorter than the old one so I took out the bent cylinder connector and put in a standard pipe and olive ring fitting which allowed me freedom to adjust the height without redoing a lot of pipework. Obviously to do this I had to also replace the straight through connector . The fact a new cylinder still used imperial fittings in this day and age did surprise me.

Thanks everyone for their help.