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persistent leak in the airing cupboard

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persistent leak in the airing cupboard

Old 27th May 2021, 18:52
  #1 (permalink)  
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Location: Berkshire, UK
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persistent leak in the airing cupboard

About a year ago I replaced the hot water cylinder in our airing cupboard after the previous one sprung a leak near to the top. The new cylinder is the same model as the previous one so the pipework was all in the right places, just a bit of spanner work needed to fit it. I did and was rewarded with a couple of slow leaks at the pipe attach points. Due to the confines of the airing cupboard it is necessary to remove the cylinder with much of its pipework still attached to it. It's like fighting with a giant set of bagpipes in a broom cupboard, needing to be twisted this way and that to extract it through a narrow doorway. Also, due to the confines of the cupboard it is impossible to see exactly where the water is seeping from, you can only just get your fingertips to the connection points to feel for water. After several cycles of fit into cupboard, fasten all pipes, refill circulating water, refill hot tap water, check for leaks then drain, disconnect, remove cylinder detach pipes etc I finally got the pipes to seal to the cylinder. It has been OK until yesterday when damp clothing was found at the bottom of the cupboard and I started the replacement again. Again, the leak was from one of the pipework to cylinder connections.

Since yesterday I have redone the pipe to cylinder connections twice with the associated fitting/testing/draining process each time. The main problem is that three of the four pipes join to the cylinder with right angled pipe elbows which screw onto the threaded stub pipes integral to the cylinder. All three of them become tight on their threads when they are not pointing in the direction that the pipes need to be at and consequently need to be undone a bit to mate with the external pipework and then they don't seal watertight. I have tried everything but cannot get a reliable joint. I first tried the ptfe tape so favoured by fitters but it came nowhere near to filling the gap between the elbow fitting and the tank when 3/4 of a turn of coarse thread away from tight. I then tried the modern equivalent of boss white jointing compound which held for a few hours before being displaced by the water pressure. Finally I used hemp joint packing with a smear of the jointing compound and after several attempts found the right wrapping thickness to seal the joint ......... for about a year.

What else can I try?

I don't know if the hot water system needs to be treated like potable (drinking) water with regard to any jointing compounds used so I have not looked at some of the better joint or thread sealers used in car oil or water systems. I might go that way soon if I don't effect a fix.

Anyone? Thanks

rans6andrew is offline  
Old 27th May 2021, 19:03
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Join Date: Sep 2009
Location: UK
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Rip it out and fit a combi boiler. you only heat the water your need however you lose the warmnairing cupboard...
6 of one half a doz of the other

Replaced mine about 5 years ago and gas usage dropped to a half and clothes still dry..

However if not suitable re make the elbows full water tight and use flexible connectors to get to the pipes not in alignment.
Kiltrash is offline  
Old 27th May 2021, 19:27
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Are your pipe fittings of the tapered type? If so, in my experience, using the teflon pipe tape, I tighten the fitting until snug, then another turn or two until the fittings are lined up. I'm sure that there are some folks on this forum with more experience than I, but I've been doing this sort of thing around the house and on boats for several decades. I think your mistake is backing off when they " ... become tight on their threads ..." Instead, you should continue to tighten at least one turn. When using the teflon tape, I wrap it tightly, but take several turns, building up a layer of tape of around 1/16 inch (about 1.5 mm) thickness. The layers of tape allow tightening "beyond snug" without splitting a fitting. Some folks wrap the tape loosely, but I've had luck with the tight wrapping. One should use care with plastic fittings, because over tightening can cause female bits to split. In things of this nature, a YouTube "how to" video can be your friend. Even better, call in a friend who has experience in this sort of thing. You can probably encourage his help by telling him that his role will just be advisory in nature and imbibing a "cool one" ... or two.

Good luck.

capngrog is offline  
Old 27th May 2021, 19:46
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Join Date: Nov 2018
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I had a small leak from a washing machine tap joint & I used LS-X joint compound so don’t know whether that would help & you can get it from screw fix, toolstation etc.
Jackjones1 is offline  
Old 27th May 2021, 19:56
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If I've learned one thing in fifty years of working on houses it's that "if you want to make it easy, make it big"

So stop fiddling around with this thing, just rip out the entire airing cupboard, install the new water heater, wait and check for leaks, then build the cupboard up around it

...and yes I'm being serious
Aaaaaaaaaaaaaaaargh! is offline  
Old 27th May 2021, 20:16
  #6 (permalink)  
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I don't know off the top of my head whether the thread(s) are tapered or parallel, I will look in the morning when I pull it all to bits, again. The elbows are brass and bought new to match with the cylinder last year when the cylinder was bought. The original fittings were quite corroded and I didn't like the look of them. I have realised since my previous reply that the water in the leaking pipe connections is not part of the potable water as it is the circulating water from the boiler and goes to the radiators as well.

rans6andrew is offline  
Old 27th May 2021, 20:20
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Join Date: Jan 2021
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When "normal" white teflon tape doesn't work, then try yellow "gas tape" for gas piping joints because that is notably thicker - friend of mine had continual leakage problems with his system until I told him about "gas tape", and that worked!!
jeallen01 is offline  
Old 27th May 2021, 20:30
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Teflon tape. Four or five turns starting clockwise at the end of the thread. Works every time: Threaded joints with stops, radiator valves, every time a coconut.
Fareastdriver is offline  
Old 27th May 2021, 20:31
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do you have Sharkbite fittings?
Aaaaaaaaaaaaaaaargh! is offline  
Old 27th May 2021, 22:01
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I suppose there is no flatted surface to get a grip on the tank connection? It is ridiculous that the manufacturers mostly don't provide it so you can hold the tank fitting against the pressure of connecting the pipes.

I use the tape. Mostly three or four turns on the thread and then twist the tape for several turns against the thread lower down to build it up a bit. Not orthodox but mostly works. You might also fit a union further down the pipe to make disconnecting and reconnecting easier. The trouble with some of the wonderful leak stop stuff in that situation is it can come back to bite you later!

I have inherited tanks in awkward places and on upper floors but nowadays all tanks on lower floors (less damage when they go) and with decent room.
ChrisVJ is online now  
Old 27th May 2021, 22:23
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Many years ago a school friends parents had a persist leak in their airing cupboard that they couldn't trace. After a period of time the discovered their son was sleep walking and confusing the airing cupboard for the bathroom...

Pipe sealing can be a nightmare.
N707ZS is online now  
Old 28th May 2021, 01:08
  #12 (permalink)  
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Leaking from the heating circuit! Bad news, that's low pressure so must be a poor thread surface - thought the temperature change expansion is more aggressive.

Building around projects is a lot easier in the US.

I'm no help at all. Mine was in a drained boilerhouse in the heart of the house so not a great problem, but I just could not accept it beating me, but it did.

I had a new IMI Supercal and plenty of access. I had years of experience. With compression fittings I'd like to use sealant on the olive and inner pipe and waterpump grease on the threads. A joy to undo years later, though now I was trying all sorts of combinations. I tried Red car sealant, the old type which I can no longer find - what was it called.
Tape. Hessian. Nothing seemed to work. I never succeeded in sealing the 22mm inserts into the tank. Okay, but not perfect. The Supercal had very think insulation so it was hard to really examine. It also soaked up the drips which made a localised mess of the fine new tank.

Yes, it would be nice if flat surfaces were offered on the tank. There is an extreme danger of causing tiny cracks in the surrounding sheet copper alloy. That is able to fool one into thinking the water is coming from the joint.

Loose rivets is offline  
Old 28th May 2021, 01:47
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I tried Red car sealant, the old type which I can no longer find - what was it called.
Hermetite (the bodger's delight!)

spekesoftly is online now  
Old 28th May 2021, 05:58
  #14 (permalink)  
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Years ago I replaced a hot water tank because one of the coil connections was leaking. Wasnít until afterwards that I realised that the nut at the base of the thread was loose. I had imagined that the nut was brazed to the tank and there to hold the threaded stub whilst making connections. It isnít! Of course, with foam insulated tanks that nut is very difficult to tighten unless you have the correct deep socket - not found in a regular socket set!
Andrewgr2 is online now  
Old 28th May 2021, 06:10
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i don't have the time to read all the answers, but my (professional) view is that teflon tape is not good and we abstain from using it. Use something like Loctite 577 or similar depending on the actual application, works all the time IF the threads and mating surfaces are physically okay. Most people don't realize how delicate the application of teflon tape is, Loctite works all the time. And 577 is one of the sealants which you can take apart later without the use of heat or similar.

As i said, i don't have the time to read everything but i hope this helps...
ThorMos is offline  
Old 28th May 2021, 06:28
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Indeed Hermetite! I seem to recall that in my youth that among other types, any Matchless, BSA, Aerial or Austin 7 engine without the tell tale red lines between mating parts was unusual - and probably dripping oil. But there was some consternation in finding examples where head gaskets had been liberally coated in the stuff because good as it may have been, it didn't cope with the higher temperatures and was a real pain to remove once it had been baked on.

As for the original enquiry, any such fitting that is tightened and then backed off - even a small amount! - is almost guaranteed to leak thereafter. Either there needs to be more ptfe so that the fitting is tightened into its final position or otherwise use a short straight coupling with an immediate elbow which could be a soldered fitting to minimise the number of inaccessible joints. If you add longer lengths to the fittings to make the connection points accessible, you can temporarily tie these to the cylinder with string or sticky tape with spacers of foam so that the fittings are not accidentally rotated when manoeuvring the assembly into place.
The application of a smidgeon of silicon sealant to the ptfe prior to it being screwed in can sometimes prove to be very beneficial...

johngreen is offline  
Old 28th May 2021, 06:36
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Originally Posted by rans6andrew View Post
.... [pipes] become tight on their threads when they are not pointing in the direction that the pipes need to be at and consequently need to be undone a bit to mate with the external pipework and then they don't seal watertight. .........
As others have said, that is never going to work, no matter what jointing compound or tape you use. You have to find a way that allows everything to be tightened-up firmly: flexible connections, or send the pipe round a loop to provide some give, or perhaps allow the tank to shift its position and chock it up?
double_barrel is offline  
Old 28th May 2021, 06:47
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My cylinder doesn't take fittings of the type mentioned, it takes a "tap connector" type fitting which can go in any orientation as the fitting doesn't turn when the nut is tightened.
UniFoxOs is offline  
Old 28th May 2021, 09:02
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How are you cutting the tape? teflon tape needs to be "snapped off / torn off" to form a raggedy edge, if you are using scissors it probably won't seal.
And are you wrapping it clockwise, because if not when you screw it in it will try to unwind from the thread, it needs to be applied clockwise

I use a product at work (niel seal), it's for water oil and fuel, it remains pliable, works with high temps and pressures.

NIEL-SEAL Gasket & Joint Sealing Compound - PSC Sealing Compounds
NutLoose is offline  
Old 28th May 2021, 09:23
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If it was me, I would have lost patience the second time the cylinder had to come out:

At that point, I would have started again and re-plumbed the airing cupboard with new pipework and fittings that aligned correctly with the cylinder connections. While doing that, I would also re-orientate the cylinder if possible so all the pipe connections were accessible in future without having to reach around the back, or having to drain and remove the whole cylinder.

Then you know it's all good and you won't have to fanny about with it ever again.

If a job is worth doing, it's worth doing well.
Uplinker is offline  

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