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Viessmann Vitodens 100 WB1A Fault

Discussion in 'Plumbing and Central Heating' started by dawson6777, 10 Jan 2017.

  1. dawson6777

    dawson6777

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    Hi Peeps, I have a fault developing on the above boiler and have had expert advise from this forum in the past, hopefully someone can help me again.
    The boiler DHW is playing up, (CH is fine though). We have noticed the hot tap (but ONLY on the Bath, which is a mixer/shower tap with wide aperture) is hot initially then luke warm. But if I throttle the tap down to a slower flow it seems to be hot again). All other taps and other shower are fine. Is this a fault developing with the flow switch possibly?

    Regards, Dawson
     
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  3. ollski

    ollski

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    What happens when you reduce the flow rate?
     
  4. JohnD

    JohnD

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    And did this behaviour stat to occur when the cold weather came?

    Typical of a combi.
     
  5. dawson6777

    dawson6777

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    The water goes warmer.
     
  6. dawson6777

    dawson6777

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    Since around Christmas time.
     
  7. JohnD

    JohnD

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    Is that a "yes?"
     
  8. Agile

    Agile

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    You need to measure the hot water flow and ideally the temperature of it.

    Tony
     
  9. dawson6777

    dawson6777

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    No not really. It was cold before Christmas too, but the boiler seemed ok then. The missus like a bath you see, but I always shower.:)
     
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  11. dawson6777

    dawson6777

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    I have just run off 5L of hot from the kitchen tap in 20 secs from a cold start and ended at 32 deg C. Very basic method!
     
  12. JohnD

    JohnD

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    A combi boiler can deliver X amount of heat. This means it can heat Y amount of water by Z degrees.

    But if you increase Y, then Z will go down, and vice versa.

    A bathtap delivers more water than a sink tap, so it will be less hot.

    If Z is, say, 35 degrees for 11 litres per minute,
    then in summer, tapwater might be (incoming main 12C plus 35C)= 47C
    but in winter, tapwater might be (incoming main 4C plus 35C)= 39C

    You are looking at a bathtap, in winter, so it is normal to be less hot.

    If your figures are like that, sadly that's just what combis do.

    However (you will have to turn the radiators off and let them go cold to check this) if the radiator pipes warm up when you run a bath, then you do have a fault.
     
  13. dawson6777

    dawson6777

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    Thanks John, I will just turn up the heat a little at the boiler and see how it goes.
     
  14. Agile

    Agile

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    You have not told us your boiler power.

    You have 15 litres per minute and no normal combi boiler can heat so much water.

    Reduce the flow rate by partially closing the water in valve under boiler.

    Reduce to 9 li/min if 24 kW boiler and 11 li/min if 28 kW.

    Then you may start to see warmer water.

    During the winter you actually need a lower flow rate but then you would need to increase to these figures in the summer.

    Tony
     
  15. dawson6777

    dawson6777

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    Thanks Tony, I will try this.
     
  16. dawson6777

    dawson6777

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    Hi Tony, Just to let you know I reduced the flow rate as advised and it see s good.
    Thankyou for your advice and also to others for their inPut.
    Regards, Dawson
     
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