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Thermostatic Bath / Shower Valve Hot / Cold Issue

Discussion in 'Plumbing and Central Heating' started by IainG, 30 May 2018.

  1. IainG

    IainG

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    Hi all,

    Reaching out in desperation :) I have had a concealed thermostatic 2-way shower / bath valve fitted for years and the shower has never worked properly. If I divert the water output to the bath tap the temperature stays constant, so works fine. However, when diverting to the shower it stays hot for a couple of minutes then goes cold, if I wait another couple of minutes it heats up again and keeps repeating this.

    - I have checked the cold and hot water pressures and they are both the same, about 2 bar.
    - I bought a new thermostat and replaced this.
    - I removed the shower head so that there was no restriction to the flow and problem still persists.

    After reading a couple of threads on here, I checked that the boiler was staying on and it is actually switching off and back on again! So this points to `flow rate` being too low according to the other threads.

    I can't figure this out though, the only difference between the feed to the bath tap and the feed to the shower outlet is up the way by about a metre including the shower hose itself. Is this really enough to reduce the flow rate so much?

    Other observation is that when the combi was put in our garage, the plumbers fed into the old plumbing route, which mean quite a distance is covered before it gets to the upstairs bathroom, including I reckon about 10 elbow fittings. So I can understand this would reduce flow rate maybe? However given the bath tap works fine this does not make total sense.

    Any help really appreciated. Dying to have showers like a normal person :)

    Iain
     
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  3. ianmcd

    ianmcd

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    which boiler do you have ?
     
  4. Combicert

    Combicert

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    Perhaps has something to do with the bore of the shower hose...? Have you tried replacing the hose to see if it makes a difference..?

    How many litres per min is coming out of the hose..?

    Are there isolators installed... are these fully open..?

    I’m not convinced the hose itself would be enough, but weirder things have happened.

    Unscrew the hose and stand there with a bucket, see if it repeats..?.
     
  5. IainG

    IainG

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    Ian - it's a Sabre 28 Combi.

    Combicert - I have just done a bucket thing, getting 8l/min at the bath tap and only 2l/m through the shower hose. I'm going to take off the shower hose like you suggest and fill a bucket from the wall fitting … watch this space!
     
  6. IainG

    IainG

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    Wow - I took the shower hose off and filled a bucket directly from the wall shower outlet - got over 7l/m. How can a shower hose reduce the flow from 7 to 2, it seems crazy. It is one of the `clean easy` hoses, smooth all over and feels like plastic, I wonder if it has a really small internal bore or something. Know anything about them?
     
  7. ianmcd

    ianmcd

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    well you have identified the problem, new shower hose time also might be a good idea to get a new shower head too.
     
  8. Combicert

    Combicert

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    Glad to have helped mate... leave a review on google... lol

    In all seriousness - some of the bores are tiny on those hoses and not really fit for purpose. I’ve seen them drop down to about 4mm.

    Grab a new hose and you’ll soon be showering like the rest of modern society
     
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  10. IainG

    IainG

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    Yes thanks for the help … hopefully my nightmare is coming to an end. Everyone in the house has been timing different parts of their showers with when the hot water comes through … only issue will be teenage kid with a full working shower ...… will cost much more to run :) Honestly I would leave a Google review or any other for that matter, but you'd need to let the technophobe know how to do it lol.

    I'll update on the result … away looking for high flow hoses and shower heads now!
     
  11. Combicert

    Combicert

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    Something like this i reckon...

    But hey, enjoy.
     

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  12. IainG

    IainG

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    Well I fitted a 12mm bore hose tonight and its giving me 5 l/m now which is a big increase on 2! Water staying hot all the time …. happy chappy. Only issue is that the hose cone does not fit fully into the holding bracket so its a bit dodgy for falling out, but rather the risk of a sore toe than a cold shower :)
     
  13. Nige F

    Nige F

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    As combicert says - some hoses have small bores from new - others large when new, can partially collapse inside and of course, not be visible outside. Similar strange things have happened to (classic ) car flexible brake pipes, causing brakes to stay on.
     
  14. Combicert

    Combicert

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    You can get a little extension thingymajigger... (if you wanted to...)

    Give me a min
     
  15. Combicert

    Combicert

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    Something like this sort of thing...

    If you were so inclined... may work better.

    Still a little disappointed with 5 lpm. I’d have hoped for a little more.

    Only one solution... new bathroom
     

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  16. DIYnot Local

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