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(Combi) Bath Mixer Tap Hot Then Lukewarm

Discussion in 'Plumbing and Central Heating' started by chaoticj, 3 Nov 2019.

  1. chaoticj

    chaoticj

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    Hi,

    We have a problem with our bath mixer tap. When you run the hot tap it does get hot for a bit but then goes lukewarm.. eventually hot again but due to the constant cycling between hot and lukewarm you can't run a hot bath.

    The central heating is off, the combi boiler is a Vaillant 835/2 E which was last serviced 18 months ago. I had to take the bath panel off so have taken some pics of the plumbing arrangement. There are no isolation valves here.

    The boiler is directly adjacent/underneath the bathroom so pipes don't travel far.. there is some kind of plumbing valve coming out of a box in the utlity where the hot pipe may run up to the bath, but it seems to be seized.. any ideas?

    Thanks in advance.

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  3. Does the same happen at other taps when you run hot only?

    Does the cycling happen if you run the hot bath tap at full flow?

    What does the boiler display panel show when the cycling is happening?
     
  4. chaoticj

    chaoticj

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    Forgot to mention, hot water control on boiler is set to max, usually run bath tap not on full as it's worse then i.e. on full it is hot then lukewarm all the time.

    When running the tap, burner and hot water symbols come on at the boiler, temperature goes up to 72 then drops quite quickly down to 50 ish..then very slowly drops off to 41. Same result upstairs on bath, sink and toilet sink taps..

    Downstairs the hot taps work fine.. kitchen tap boiler hovers around 55, utility 60 and water is very hot, steam comes off!

    So it seems the boiler is running 15-20 degrees less when supplying the upstairs taps.. what does this mean??
     
  5. Chris_W

    Chris_W

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    When running the hot tap, does it pulse out, or just run full
     
  6. chaoticj

    chaoticj

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    Hi The Novice, I don't think the water pulses out, it drops off a bit after you turn it on.
     
  7. Chris_W

    Chris_W

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    Quarter turn tap or traditional screw down tap? Is this a new fault or pre-existing?
     
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  9. chaoticj

    chaoticj

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    I think the bath taps are screw down but not sure? They look quite old?

    Always seems to have been a problem but we have only been here 12 months.
     
  10. Couple of possibilities - get a decent RGI to look at the boiler
     
    Last edited by a moderator: 3 Nov 2019
  11. chaoticj

    chaoticj

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    Hi,

    I contacted Vaillant who repaired the boiler originally, they said the engineer on their visit picked up that we could potentially have "an issue with the circulation of water around your system".

    First we have heard of it.. what does this mean exactly? I don't believe there is a hot water pump, does it mean the hot water pipes are blocked somewhere?

    Thanks in advance.
     
  12. ianmcd

    ianmcd

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    Do you have a mixer shower anywhere
     
  13. chaoticj

    chaoticj

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    Nope, just a single electric shower in the bathroom. The bath has a mixer tap with the top blocked off so it looks like there was one in the past.
     
  14. ianmcd

    ianmcd

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    OK let the CH cool down or do this test when the CH is off, with the CH pipes cold run a hot tap and feel the CH flow and return pipes below the boiler and see if either is heating up
     
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