New Shower Running hot and cold

Discussion in 'Plumbing and Central Heating' started by chrisfuz, 8 May 2005.

This topic originated from the How to page called Installing a shower.

  1. chrisfuz

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    I have a combi boiler and have just installed a new shower. The mixer says it is OK for combi boilers but when I use the shower it runs hot and cold. My water pressure is good. No other appliances or taps were being used while showering. :?:
     
  2. ChrisR

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    MOre details please, on combi inc age, and mixer type?
     
  3. PEDANTICVINDICTIVEMAN

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    You might end up having to run the hot basin tap to keep the boiler firing while showering during summer months.
     
  4. xbond

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    You may be exceeding your boiler's maximum flow rate, try to reduce the flow...
     
  5. Moley

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    As you have a combi i'm guessing that you have a thermostatic mixer valve. Have you checked that the hot and cold supplies are connected the right way around? Thermostatic mixers dont like the supplies connected round the wrong way, just a thought... :idea:
     
  6. chrisfuz

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    The Combi boiler is an Ideal CF65 or 75 I think. Don't know how old it is at least about 4 years

    Shower mixer is this one.

    http://www.screwfix.com/app/sfd/cat/pro.jsp?ts=35889&id=19454

    I'm sure its connected the right way round as red goes hot blue goes cold. Hard to check actual pipes as it is now plastered into the wall behind some tiles.
     
  7. ChrisR

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    The combi doesn't sring to mind, but the most likely source of your problem is sludge/scale in the secondary heat exchanger. They all do it eventually.
    If you had your supplies reversed you would get only hot water or only coldwater, typically - at least that's what I got when I did it!

    Thescale slows the temperature - sensing down so the combi turns off for long periods to get the temp down, WHen they're clean they switch on and off quickly enough that you don't notice the variation.

    Not sure which type of 2ndry h/e you'll have, but they're all descalable with more or less difficulty. They have to be taken out though, as a rule.
     
  8. PEDANTICVINDICTIVEMAN

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    Try running the hot tap on the basin and then turn on the shower valve to approx temp position you would normally use it at, then leave it a while to stabilise and see if it solves the problem, a different shower head letting the right amount of water pass throught the boiler may sort the problem, it has on mine.
    Of course if your combi is an old one and doesn't modulate, you could be up shiiitte creek without a paddle.
     
  9. cobra

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    Does the boiler fire when you turn on shower and does it keep cutting out and restarting- if so could be boiler thermostat cutting out due to faulty stat or scale in heat exchanger or it could possibly faulty thermostatic mixer
     
  10. Bambi

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    Does the water run hot and cold elsewhere, such as the bath. I had this problem and it turned out to be the heat exchanger. It was removed, cleaned and then worked OK. It could be sludged up with scale or debris from a new install. The system may need flushing too, to ensure it don't sludge up again.
     
  11. ChrisR

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    Forget it guys, this post's over a year old!
     

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