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Discuss Stupid questions from a novice in the Fittings & Pipes area at

  1. David Mitchell

    David Mitchell New Member

    I have a couple of stupid questions. (Actually, more than a couple, it turns out).
    Firstly, PTFE tape. Is it worth it (a lot of people recommend it; but many say it makes no difference. Who is right)? Is it stable enough to be used on the piping for the default radiator? What about the fittings on the back of the stove? Intuitively it seems to me that no part of the stove directly connected to water should ever get above 100 degrees, so PTFE tape would be okay. Is that right?
    Secondly, one of the plumbers we had in to quote suggested that we could handle filling the system, and dealing with overflow due to expansion, by teeing off from the default radiator flow piping, into a small tank with a ball-cock inlet, and overflow pipe outlet.
    That seems entirely reasonable, but I've never seen anyone else suggest it.
    Am I missing something?
  2. Darren Jackson

    Darren Jackson Plumber GSR

    Firstly PTFE is the best thing if used correctly on male threads such as radiator tails and boiler/cylinder & tank tappings It has to be wound round a good few turns the correct way clockwise so it does not strip off when tightening the joint up. A Lot of amateurs use it on compression fittings but that is not needed and can infact be a bad thing.

    Secondly You should already have a vent for expansion! what are you trying to achieve? and what kind of system do you have? Or is this a new install?
  3. David Mitchell

    David Mitchell New Member

    Okay, with respect to PTFE, I was advised to use it on compression joints - why is it wrong?
    The system is a new one - the diagram I have from the stove manufacturer has a vent on the flow, and an inlet tank on the return - the plumber I had in to quote for installation suggested that I combine the two, tee off from the inlet with an overflow into the tank; but I can't see a reason to do that except that the inlet tank might reach the temperature of the flow feed rather than the return feed.
    I can post a diagram if that would help.
  4. Darren Jackson

    Darren Jackson Plumber GSR

    Compression joints only need to be tightened up by hand and then usually just need say and extra half a turn to nip up the olive and do not need any PTFE on them at all, if there is a little weep on it then just give it another quarter turn with your spanner. Overtightening a compression fitting will crush the olive and it will leak. Using PTFE on a compression joint is not good practice although we come across it all the time usually because it is leaking and we've been called out to it,

    Always follow the Mi's to the letter if they show it on a diagram how they want it doing, then have it done just like that. Deviating away from the Mi's could be dangerous & invalidate any warranties and leave you up the creek!
    • Agree Agree x 3
  5. Stanios

    Stanios Plumber GSR

    I've always been told about overtightening olives but so far I've only managed to crack a few nuts never had a smashed olive.
  6. Darren Jackson

    Darren Jackson Plumber GSR

    It's usually a cracked nut when PTFE has been used lol. but the olive can easily be crushed if over tightened not cracked.
  7. Ric2013

    Ric2013 Plumber Top Contributor!!

    If it's an uncontrolled heat source, e.g. a woodburning stove with a backboiler and with manual or thermostatic controls and not a computer and electronic devices etc., and your installer is suggesting you combine the vent and cold feed, then you really need to find another installer. One with HETAS or OFTEC (or equivalent) wet heating systems solid fuel competent person registration would be best - then you don't need to inform Building Control. The one you have is giving dangerous advice.

    Combined vent and feed is a safety compromise and ONLY acceptable where the manufacturer has specifically stated that a combined feed and vent is acceptable practice, usually because the boiler itself incorporates advanced safety devices.

    PTFE: yes, it's alright on screwed joints. Hemp and paste is better though (not suited for drinking water), Loctite 55 is also very good, easier to use, more reliable than PTFE, and can also be used on drinking water. For an amateur who doesn't need a tin of paste going hard, I'd say Loctite 55 is the best.

    PTFE on compression (just a couple or so of turns on top of (i.e. around) the olive) can work as a temporary measure where there is a buggered overtightened olive causing a weep (installed by others) and it's 5 o'clock and you want to get the water back on for the weekend prior to a proper repair on Monday. That's when I'd use it myself.

    Don't use it on the threads of a compression joint EVER. I note Anglian Water subcontactors seem to like to put it around the olives and I wouldn't say it's wrong. But it's not pretty and I wouldn't put my name to it as a permanent installation for that reason.
    • Agree Agree x 1
  8. David Mitchell

    David Mitchell New Member

    Thanks for the advice - I think I've been overtightening my compression joints so far - I'll tone it down for this project. As to warranties, it's a second hand stove, so there are none :-(
  9. jtsplumbing

    jtsplumbing Plumber GSR

    So installing it without any instructions could be a big mistake as it seems both you and your 'Plumber' don't have much of an clue and are guessing at things
    • Agree Agree x 2
    • Funny Funny x 1
  10. David Mitchell

    David Mitchell New Member

    I don't understand the difference between what the manufacturer is proposing, and what the plumber suggested. In either case the heating system can handle expansion due to heat. I've attached two files, the more complex one is what the manufacturer recommends, the other is what our plumber suggested.

    heating system version 2.png

    heating system.png
  11. bogrodder

    bogrodder GSR

    I beg to differ, compression fittings with brass olives definitely need either a smear of paste or a wrap or two on the meeting face of the olive ti that of the face of the fitting.
    As a matter of fact I don’t know of any old school time served plumber that doesn’t paste or wrap the olive. Fittings are terrible these days ,that you need a helping hand to just about guarantee a decent joint.
    • Agree Agree x 2
    Last edited: Feb 2, 2018
  12. king of pipes

    king of pipes Trusted Plumber GSR Top Contributor!!

    Smear of paste on all mine very rarely get a problem. Cheers kop
    • Agree Agree x 5
  13. Best

    Best Trusted Plumber Top Contributor!!

    Your plumber is an idiot.
    Do NOT use that guy to plumb your stove!
    Open vent gravity circuit solid fuel systems need a feed from return primary and a vent pipe from flow primary and each 22mm minimum. Both also act as safety vents
    Sounds to me your plumber never has done any solid fuel work before.
    For compression olives you need paste and for male threads into rads and boiler ptfe tape used correct amount of turns is absolutely fine and in my opinion some paste on the taped joint will also help.
    Ptfe can take any heat a heating system can put on it.
    Hope you are not going to do the solid fuel work yourself?
    • Agree Agree x 1
  14. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    Paste for me as well
  15. Vee

    Vee Plumber GSR

    Paste can help. Never PTFE on compression. Amateurish DIY practice. I am time served and do not use pasts unless absolutely necessary. PTFE is for threaded joints only.
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