02GF74
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 posted on 10/12/20 at 10:44 AM |
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making plumbing joins
On Saturday I'm about to embark on replacing an indirect hot water cylinder for a friend. There a 4 pipes to connect as well as fitting the
immersion heater.
I've plumbed in taps and cisterns before and it was a matter of doing up the connections tight but to guarantee the connections do not
leak, should I use PTFE tape and jointing compound (whatever that is) or both?
Access is not easy and I don't live there so going back to fix leaks is to not going to be easy/convenient.
Thanks
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40inches
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| posted on 10/12/20 at 10:55 AM |
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I always use PTFE tape or liquid on any copper compression joint.
Liquid
[Edited on 10-12-20 by 40inches]
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nick205
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| posted on 10/12/20 at 11:23 AM |
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On compression joints I generally use a bit of PTFE tape wound carefully the right way round the thread. Leaks are a PITA in your own home let alone
a job you've done somewhere else. I also make sure the pipes are dry externally once the joint is made and then wrap a bit of tissue (toilet
roll) round the joint when turning the water back on. Damp tissue is always a good indicator of a leaky joint before you leave.
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gingerprince
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| posted on 10/12/20 at 11:55 AM |
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I assume it's a vented cylinder you're replacing? If it's unvented, then it'll be illegal and very dangerous and you
shouldn't touch it (or you could blow yourself and the house up!). If it's vented, then assuming you're not a registered installer
( which given you're asking whether to use PTFE or not I suggest you're not  ) then in theory building control will need to be informed
to make sure the new cylinder installation meets current requirements. The latter probably won't become an issue until they come to sell their
home and the solicitors stick their oar in.
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02GF74
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| posted on 10/12/20 at 12:21 PM |
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thanks for that - it is vented as it has feed from cold water tank in the loft.
so noone uses jointing compound then?
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40inches
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| posted on 10/12/20 at 12:35 PM |
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quote:
Originally posted by 02GF74
thanks for that - it is vented as it has feed from cold water tank in the loft.
so noone uses jointing compound then?
PTFE liquid is more of a jointing compound than a true liquid. It will seal largish gaps.
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SteveWalker
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| posted on 10/12/20 at 02:12 PM |
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The connections to the tank itself will probably be 1" BSP and either male or female, so you'll need PTFE tape or a sealant for those
fittings.
If you are using compression fittings to connect to the pipework, I'd not use any tape or sealant, as compression joints are designed to work
without and tape or sealant can cause problems (although unlikely). I always prefer to use copper olives rather than brass in the fittings though, as
brass is hard and sometimes doesn't deform enough to give a really good seal and a tight grip.
Alternatively, why not use decent quality push-fit fittings? They are perfectly suitable for this use; have an O-ring to seal properly to the
(de-burred) pipe and are quick and easy. We fitted some to a holiday home in France (with extremely high water pressure) and they were still
leak-tight when the property was sold recently, after 28 years. I have a few in this house, where access was a problem, although I mainly prefer
soldered joints.
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Mr Whippy
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| posted on 10/12/20 at 03:34 PM |
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If your pipe is smooth and the olive undamaged, compression fittings will not leak and there's no need for PTFE tape or anything else. Tbh your
better using solder joints unless you intend on making the section removable, they are cheaper and will never ever leak.
When fitting the immersion heater use the correct ring spanner their not much cost as you'll be able to tighen it up correctly and use PTFE tape
on that and the washer or it will leak. Another thing to keep in mind is how are you going to drain the system in the future...? you need to fit ball
valves for the bottom of the tank and the lower point of the heating coil, it's funny how often these are missed off
[Edited on 10/12/20 by Mr Whippy]
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SteveWalker
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| posted on 10/12/20 at 07:40 PM |
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No drain valves on my HWC, but draining the coil is just part of draining the central heating, so using a nearby radiator drain valve works fine for
me. The last time I needed to drain the cylinder (to replace it), I just opened up a top connection and syphoned it out.
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perksy
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| posted on 10/12/20 at 08:35 PM |
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Use copper olives if you can, PTFE tape is fine as long as you don't go beserk with it
We don't use jointing compound of drinking water installations due to contamination risk (We can't use flexi's either on taps for
the same reason)
Use soldered joints wherever you can (pre soldered ones where your not happy to do your own)
Push fit is fine but we inspect annually especially if their braided hoses as when they fail, they fail big time 
(they seem happier of cold water fed pipework as there's no heat cycling)
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jacko
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| posted on 10/12/20 at 09:18 PM |
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It probably won’t leak but if it dose and say a sealing comes down I hope you have insurance
My dad had a leak and it cost a fortune to put right
I’m not saying your not capable to do the job it’s just a little warning
Jacko
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BenB
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| posted on 11/12/20 at 11:33 AM |
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As has already been said you shouldn't actually need PTFE on the thread of a compression joint as it's not supposed to be the bit holding
back the water! A properly cut and inserted pipe and an olive does that. Lots of people fail to cut the copper properly (e.g. using a hacksaw) and /
or fail to ensure that the end of the copper is properly engaged with the end-stop inside the compression joint. Sticking some on as insurance
isn't a bad idea but it shouldn't be necessary.
I'm surprised about the comments re not allowing flexi's for drinking water considering how many kitchen taps come with them. Equally
I'm always happy when I can do an install without using flexi's and at work (an NHS property) we were told point blank they weren't
allowed to be used (at all). Then again (with good reason) NHS Property services tend to be exceedingly cautious. I remember when I was in hospitals
two people died from Legionairres disease in my ward. It transpires over the years they had taken a spur off a hot water pipe and then further down
the pipe done the same and then joined them together creating a nice little bypass loop. Therefore hot water took the path of least resistance (IE
down one branch of the parallel pipes) and the other just sat at body temperature breeding bacteria which it would slowly dose the downstream hot
water with. Unfortunately one of the first pipes after the reconnection was the shower in a mixed oncology and respiratory ward (IE bad lungs and bad
immune systems). Simple mistake but tragic consequences.
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perksy
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| posted on 11/12/20 at 09:10 PM |
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quote:
Originally posted by BenB
I'm surprised about the comments re not allowing flexi's for drinking water considering how many kitchen taps come with them. Equally
I'm always happy when I can do an install without using flexi's and at work (an NHS property) we were told point blank they weren't
allowed to be used (at all). Then again (with good reason) NHS Property services tend to be exceedingly cautious. I remember when I was in hospitals
two people died from Legionairres disease in my ward. It transpires over the years they had taken a spur off a hot water pipe and then further down
the pipe done the same and then joined them together creating a nice little bypass loop. Therefore hot water took the path of least resistance (IE
down one branch of the parallel pipes) and the other just sat at body temperature breeding bacteria which it would slowly dose the downstream hot
water with. Unfortunately one of the first pipes after the reconnection was the shower in a mixed oncology and respiratory ward (IE bad lungs and bad
immune systems). Simple mistake but tragic consequences.
I work in NHS Estates and Flexi's aren't allowed, We pipe up in copper
Dead legs aren't allowed either and we also lag all supply pipework to stop heat transfer and as you'll know if you don't keep the
water both moving and the right temp' you can have big problems
The reg's are stringent in an NHS environment and rightly so
Apologies to the OP, We've gone off topic a bit
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