Help with hot water please

Discussion in 'Painters' Talk' started by Colinandcarole, Nov 13, 2018.

  1. Colinandcarole

    Colinandcarole New Member

    Hi
    We have a brand new Bosch green star 38 cdi boiler fitted by plumber

    However it takes ages for hot water to flow through tap ( it is good and hot when it does) regardless of proximity to boiler

    As we are in a low pressure area we had a booster pump fitted so flow into boiler is good

    Is this something just to learn to live with or can some adjustment be made in the boiler? — the eco button is set to off

    Any advice much appreciated

    Colin
     
  2. Allsorts

    Allsorts Super Member

    Turn the eco button on.*

    And read the instructions :)

    I'm guessing the eco button enables/disables the 'pre-heat' feature - this will fire up the boiler for a few seconds every few minutes or so (don't know the actual timings) which means the boiler is always hot and ready to go.

    Otherwise it needs to heat up from cold every time the hot tap is opened.


    EDIT: *OOPS! I read that wrong. The 'eco' button is 'off' so theoretically the pre-heat is 'on'.

    Hmm, Mike's point below is a good one.
     
    Last edited: Nov 13, 2018
  3. Mike83

    Mike83 Screwfix Select

    If it’s new pipework from the boiler to the taps then there may be an issue.
    But if it’s old pipework 22mm then all the cold water in the pipework needs to come out the tap before any hot will.
    So basically a high volume of water needs to pass before it gets hot.
     
    Allsorts likes this.
  4. Allsorts

    Allsorts Super Member

    Bottom line - this is a brand new boiler fitted by a plumber, so if you've covered all the obvious points then there may be a further issue that he should come out to sort.

    You say you have a mains booster fitted - what kind is this? Is it a wee 12lpm unit that fires up whenever there's demand? If so, I wonder if this adds a further delay to the whole caboodle?
     
  5. All the eco function does is burn gas and give you a higher bill starting the boiler every 1/2 hour or so 24/7.

    It heats the water in the heat exchanger, you get this little bit of water then it runs cold again until the boiler heats more water,this will then run constant.

    Save money and turn on the Eco function so the boiler only fires when you need it.
     
  6. Colinandcarole

    Colinandcarole New Member

    Hi thanks the pump is a salamander 12 fitted next to main stop cock firing up on any demand — sadly we live in a very low water pressure area
    Would it be better to fit near the combi?
    Colin
     
  7. Colinandcarole

    Colinandcarole New Member

    There is a mix of pipes — when I rang Bosch I got the impression there was something that could be ‘tweeked’ Only by the installer— have you heard of this??
    Colin
     
  8. Mike83

    Mike83 Screwfix Select

    Tweeked.
    Probably the flow rate.
    Won’t make any difference to how long hot water takes to emerge from the tap. If anything it will take longer.
    The hot water exits the boiler at 15mm, if it was all 15mm then things would be fine.
    Any 22mm runs hold double (guess)the volume a 15mm does.
    So even though you turn on a tap and the boiler fires, there’s lots of cold water in the pipes that needs to come from the tap before hot will.
    Sometimes combi location in relation to the existing pipework can cause small issues.
     
  9. Allsorts

    Allsorts Super Member

    Colin, do you have a further £1k to spare? Does Carole?

    Cool - get ready to spend it :)

    You have a LARGE combi boiler at 38kW, usually chosen for larger properties and even for a possible 2-simultaneous shower performance. It's a beaut. It can deliver over 16lpm of hot water!

    It's a cracker!

    And it's being fed by a Salamander which can not deliver over 12lpm (it isn't allowed to), and this 12lpm is shared by the hot and cold taps in your house.

    A combi like that would expect around 20lpm to be available on its inlet, delivered at 3bar plus. You are providing it with significantly less than it can even heat.

    Ok, I don't know if this is what's behind your issue - I am not a plumber or GasSafe - but I do suspect that your current setup is unsatisfactory. Pointless.

    Crazy.

    Nuts, man.

    The whole idea of a combi that size is that is can heat large quants of hot water, whilst your mains supply has reserves for the cold - so that you don't roast in your shower. For a combi like that to be heating 16lpm of hot water, you would want - ooh - a goodly 8-odd of cold to also be available. At the same time.

    You have 12lpm max - shared.

    I suggest you ask WB for their advice. Based on this, you need to have a chat with your plumber.

    There is a solution, but it'll take up a bit of room - a pumped accumulator like the Challis CB+250 (or Salamander or Grundfos equivalents). These WILL cure you poor water supply problem - they are superb - but I cannot be certain that it'll also sort your boiler's weak performance. But good chance it will.

    I suspect your HUGE boiler is simply responding to the poor flow available to it and is throttling back to accommodate. Possibly.
     
    Mike83 likes this.
  10. Mike83

    Mike83 Screwfix Select

    Colin I’m guessing the boiler is working.
    But the main issue you have is the time it takes to deliver hot water to the taps from the moment the tap is opened.
    This is normal for a combi to suffer from this.
    Sometimes it just takes a few seconds other times a fair bit longer.
    Just because the combi is close to a kitchen or bathroom it doesn’t mean the pipework will take the shortest route.

    The boiler does seem oversized as Allsorts states.
    But Allsorts,Colin does say he’s happy with the water performance once it does come through the tap.

    A bit clarification from Colin on what his exact issue is incase I’m mistaken would help.
     
  11. Colinandcarole

    Colinandcarole New Member


    Thanks
    The main issue is the waste of water —we can fill a 4lt bucket while waiting for kitchen tap to get hot— boiler is on floor below!!

    When water runs hot it is great and we have good hot strong showers

    Colin
     
  12. Mike83

    Mike83 Screwfix Select

    Welcome to the world of combis.
     
  13. Mike83

    Mike83 Screwfix Select

    This is the problem with combis.
    So much waste. Also if you run a bath and turn the hot on and off frequently you get bursts of hot and cold from the hot tap.
     
  14. Mike83

    Mike83 Screwfix Select

    So your running the tap for almost 20 seconds before you get any hot water. If the pipe diameter was smaller (15mm)the amount of wastage would be reduced and hot water would come quicker.
     
  15. Mike83

    Mike83 Screwfix Select

    Even though the boiler is close to the sink it may not be tee’d in under the sink.
    If you had an old water tank it could be tee’d in there.
     

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