1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Boiler starts up when cold water taps switched on

Discussion in 'Plumbing and Central Heating' started by Gammy leg, 31 Oct 2017.

  1. Gammy leg

    Gammy leg

    Joined:
    31 Oct 2017
    Messages:
    30
    Thanks Received:
    1
    Country:
    United Kingdom
    Hi,

    I had new Viessman Vitodens 100 combi boiler and central heating system ( incl rads and all pipework ) installed last December and I've recently become aware that routinely ( but not always ), whenever the cold taps are opened, the boiler kicks in and starts heating the hot water.
    Is this normal, and if so, why? Seems a waste of gas if I'm not using the hot water.

    If it makes a difference, the boiler is currently set on ECO which as far as I can gather means that it doesn't store a reserve of hot water for quick release.

    Thanks
     
  2. DH6

    DH6

    Joined:
    16 Jul 2011
    Messages:
    453
    Thanks Received:
    69
    Location:
    Durham
    Country:
    United Kingdom
    There will be a 'dead' leg on your hot water supply somewhere in your property. Opening and closing a cold tap quickly ( usually happens more on 1/4 turn taps ) compresses the air then releases it resulting in the boiler recognising what it thinks is a hot water demand.

    To rectify remove the dead leg.
     
    • Thanks Thanks x 1
    • Like Like x 1
  3. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    5,688
    Thanks Received:
    763
    Country:
    United Kingdom
    As above. But the dead leg could just be a tap that's never used so check there first by trying all the hot taps.
     
  4. Echo the husky

    Echo the husky

    Joined:
    25 Mar 2011
    Messages:
    2,474
    Thanks Received:
    324
    Location:
    Devon
    Country:
    United Kingdom
    I've had this for weeks home here due to a section of unfinished pipework that is part of the cloak room alterations, I finally installed the rest of the pipework yesterday and could bleed the air out with the iso valves.
     
  5. Gammy leg

    Gammy leg

    Joined:
    31 Oct 2017
    Messages:
    30
    Thanks Received:
    1
    Country:
    United Kingdom
    Thanks guys, I do indeed have a 'dead leg' in the hot water system under the kitchen sink. It's a pipe about 2' long with a blanking cap on the end, a left- over from the original system. Never though something so simple could cause this to happen.
    I'll take a look at the weekend and modify to eliminate it.

    Cheers.
     
    • Like Like x 1
  6. AGAS

    AGAS

    Joined:
    21 Feb 2014
    Messages:
    9,625
    Thanks Received:
    1,688
    Location:
    down south
    Country:
    United Kingdom
    Fit a mini expansion vessel on inlet to boiler if access not available to dead legs
     
  7. gasbanni

    gasbanni

    Joined:
    7 Jan 2007
    Messages:
    7,712
    Thanks Received:
    823
    Country:
    United Kingdom
    The dead leg might have been put in to stop water hammer ......It was an old trick not correct now. Against the regs
     
  8. Gammy leg

    Gammy leg

    Joined:
    31 Oct 2017
    Messages:
    30
    Thanks Received:
    1
    Country:
    United Kingdom
    OK,

    Finally got round to removing the dead leg in the kitchen and it made no difference. After a quick check, remembered there is another redundant section in the bathroom where the shower will be fitted once the tiling is completed.
    Purged this section of air and now all is working perfectly. No unwanted boiler start-ups.

    Thanks to all who gave advice.

    Gammy
     
    • Like Like x 2
  9. DIYnot Local

    DIYnot Local

    Joined:
    3 Sep 2019
    Country:
    United Kingdom

    If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

    Select the supplier or trade you require, enter your location to begin your search.


    Are you a trade or supplier? You can create your listing free at DIYnot Local

     
Loading...

Share This Page