Installing TRV without draining the system

Discussion in 'Plumbers' Talk' started by leekumkee, Nov 27, 2017.

  1. leekumkee

    leekumkee New Member

    Hi all, as above is it possible to install TRV's without draining the system?

    I got two radiators downstairs without TRV on them. My water and heating is run by a combi boiler. Each radiators got two lockshield on them so the only way for me to open/close the rads is by manually opening one of each lockshield, and I do this everyday, everytime. I'm hoping by installing TRV's on them would help me regulate the heating.

    I am thinking to do one of the rads first as the other rad is not being use anyway.

    Thank you in advance. Any help and tips would be appreciated.
  2. KIAB

    KIAB Well-Known Member

    Freeze it.
    leekumkee likes this.
  3. The Teach

    The Teach Well-Known Member

    There are tricks of the trade to exchange water valves without full drain down.

    once you let the pressure out,with the rest of the system water held in suspension and working PDQ it can be done (you will need to exchange the valve in less than a minute).

    sometimes the existing radiator and pipe nuts can be reused.
    leekumkee likes this.
  4. KIAB

    KIAB Well-Known Member

    And if it goes pear shape,you can end very wet.:oops:
  5. The Teach

    The Teach Well-Known Member

    Very wet indeed :oops:
  6. leekumkee

    leekumkee New Member

    @The Teach,

    I had a look and it seems I can still use the existing pipe and nuts, I just need to replace it with the same TRV valve size, which Screwfix have them. I'm not sure what you mean by PDQ ..
  7. leekumkee

    leekumkee New Member

    Cheers @KIAB, I will search and read more about your suggestion :)
  8. The Teach

    The Teach Well-Known Member

    Pretty Darn Quick !
    leekumkee likes this.
  9. KIAB

    KIAB Well-Known Member

    Electric pipe freezer can be hired, advantage you don't have to rush, can leave frozen if you encounter a problem, or you can feeze from a can, ice plug should last around 30 minutes.
    leekumkee likes this.
  10. leekumkee

    leekumkee New Member

    I have stumble upon this youtube video and thinking to follow his steps, but instead of opening the rad valve I'm thinking to keep it closed to prevent water from dripping while installing a TRV valve. Am I right with my assumptions? Also, do I actually need a jointing compound or a PTFE tape is enough?
  11. Hi Lee.

    Is you system a combi (sealed) or conventional (with a small F&E tank in the loft)?

    If the former, then it's surprising how little water comes out an open pipe - once you've de-pressurised the system, of course.

    This is because - being a 'sealed' system - air has to get in to the system via the same open end to replace the water that's trickling out, and it would have to find its way back up the pipe the water is coming out of. In practice, water only trickles, or sometimes small-'glugs', out, but is fully containable.

    If it's a vented system, then a similarish result can be had by blocking the feed in the F&E tank, and also the open vent pipe above. But this tends to be less successful.

    If it's combi, then I would say 'def go for it':

    You ideally need a flat tray to place under the valve (say the upturned lid from a storage box), lots of towels and sheets just in case. Actually, a plastic sheet - even a bin-bag - first would make sense, lined and rasied-edged with towels.

    You then get your TRV which you have checked is an exact match in length so you'll know it'll be a straight swap...

    I'd use jointing compound (eg Fernox Hawk White) rather than PTFE tape - more reliable, and a lot easier to apply.

    Shut off both rad valves fully. Open the bleed screw in that rad to release stored pressure - then re-close. Go to another rad (which has both valves at least partly open) and also release the pressure from there via the bleed screw - that'll de-pressurise the rest of the system - possibly around a cup of water will come out doing this - possibly more).

    Prepare the new valve by removing the nuts and olives and smearing the thread with comp. Does the 'rad' end have a rubber O ring? If so, that should be enough to seal it, so no compound on that - but silicone grease would be good if you haver any (every home should..)

    Slacken off both existing valve nuts but don't fully undo yet. Ensure the valve is 'loose' - can be rotated easily. Water will be coming out, but you should be surprised at how little - keep mopping this up whilst you undo each end to test the 'flow'! You should find it's all totally manageable.

    Ok, what you'll find is, once any remaing stored pressure has released, then very little - perhaps no - water will come out as long as the valve is on the pipes, even tho' it's very loose. This is because air can't easily get back in past the valve fitting. Of course, once the vale is fully removed then some water will then come out, but you'll (hopefully) be surprised at how little. Do a test run - slip off one end almost all the way and see! Get it back on! Now the other end...

    Ok? Looking gooooood?

    Cool - calmly remove it and slip on the new. Nice - that took you only 6 seconds! And hardly any water came out! And immediately the new valve has been slipped on - before the nuts have been done up - any water has stopped!

    Cooooool. One more thing to do - ease the pipe end out until you can see the olive, and wipe a smear of Fern over it. Push back on and lightly do up the nut.

    Do up. Open valves. Re-pressurise system. Bleed the rads. Also check nearest rad for air.

    Run the system and check all rads for air. (Bleed with boiler off).

    Ok, and if you could video this for us, that would be great. :rolleyes:
    leekumkee likes this.
  12. DIYDave.

    DIYDave. Well-Known Member

    9” roller trays work brilliantly in this situation, tuck up under rad valves and close to skirting. Still good to put old towels underneath for any spills

    I keep 2 old trays for this purpose and great when fully draining a rad. In the above case, there should be much water at all to catch but better to be prepared!
  13. retiredsparks

    retiredsparks Well-Known Member

    Don't you just love the way plumbers use pipe grips/ vicegrips and stilsons on highly polished chrome plated fittings.
    leekumkee likes this.
  14. nigel willson

    nigel willson Well-Known Member

    Done it many times , but you need to know the pitfalls and have a backup plan! And some caps/ blanks ready.
    leekumkee likes this.
  15. nigel willson

    nigel willson Well-Known Member

    Piece of cardboard!
    leekumkee likes this.
  16. A revision to my post#11 above (now I've watched that vid.)

    It probably makes more sense to drain the rad fully first, as shown on the vid. This way you only have one joint to actually worry about, and it's the one that'll be letting out less water.

    Once the new valve is on, your system will then need a lot more filling than before - the whole rad needs doing.
    leekumkee likes this.
  17. dubsie

    dubsie Member

    You snatch them but you still need to take the pressure off, to be honest I drain down and then use my wet and dry vacuum directly blow the valve to suck the left over water
    leekumkee and Dave does Gas like this.
  18. No danger in your life, then. Pfffft.
    leekumkee likes this.
  19. leekumkee

    leekumkee New Member

    Hello all, just updating this thread!

    Thanks to everyone who shared, posted and given their valuable knowledge and experience in my situation. I manage to changed and installed TRVs on my two radiators, they seem to work as normal and without problem. Cheers to all! :)

    I got a follow up question, on my estimate I think I lost 500ml of water on each radiator, should I need to top it up with inhibitor?

    @Devil's Advocate, unfortunately I didn't manage to record a video of it, its hard when you got kids running around and insisting to HELP you :)
    Deleted member 33931 likes this.
  20. Nice job.

    No vid! I'll have to use my imagination, then...

    If you are confident that your system was fully treated with inhib, you should be fine. Any doubts, and it's worth adding.

    Do you have a magnetic filter on the return pipe before the boiler? If not, there's your next project :)

    (And it makes it easy to add chemicals, etc...)

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