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

Combi Boiler or Conventional?

Discussion in 'Plumbing and Central Heating' started by Naz1977, 17 Jan 2018.

  1. Naz1977

    Naz1977

    Joined:
    22 Nov 2016
    Messages:
    174
    Thanks Received:
    4
    Country:
    United Kingdom
    We have a small bungallow, and it has a Worcester Bosch 30Si combi boiler.

    As the bungalow is now, it only has a single bathroom with electric shower and kitchen with Sink.
    We also have a washing machine and dishwasher.

    Problem we have is that the water pressure is shocking. We have problems with both cold feed and hot feed, although hot feed is the worst.

    I have always hated the combi boilers, but as this is a boiler that was here when we bought a house, then have had no choice up to now.

    We are planning on doing an extension above, and I was thinking as we are doing this now, we might as well replace the boiler.

    So my question ( before I get a gas engineer in to have a chat with me officially) :

    As there will be small loft space at the top, can I just get a new conventional boiler, with cylinder in the loft to get rid of the pressure issues?

    If I do that, and have all 3 units ( boiler, cylinder and overflow) in the loft, does that then give me a better pressure around the house? I am thinking if I do that, then I can have a pumped shower upstairs and leave the electric as it downstairs. Nothing is worse than a horrible low pressure shower.

    I am pretty sure that the 30Si as it is at the moment, will not be man enough to run another 5 radiators and a new bathroom.

    Any help appreciated
     
  2. Sponsored Links
  3. bernardgreen

    bernardgreen

    Joined:
    3 Nov 2006
    Messages:
    25,823
    Thanks Received:
    2,571
    Location:
    Bedfordshire
    Country:
    United Kingdom
    If there is space for a cylinder then a combi is not necessary.

    A cylinder provides the benefits of an airing cupboard.

    Many combi boilers are very in-efficient when producing small quantities of hot water.

    Building Research Establishment evaluation of "High Efficiency" boilers produced these results,

    bre tapping efficiency_1.jpg
     
  4. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    6,370
    Thanks Received:
    883
    Country:
    United Kingdom
    True but that's hardly a selling point, since you can get more benefit for less by putting a radiator in a cupboard without half the space taken up by a cylinder and with the ability to turn it off when it's not needed
     
  5. Naz1977

    Naz1977

    Joined:
    22 Nov 2016
    Messages:
    174
    Thanks Received:
    4
    Country:
    United Kingdom
    I don't think there will be any room for an airing cupboard on the top floor. The most we will have will be a small loft space that can house the boiler and cylinder and overflow. Is there any issues with putting cylinder in the loft?

    I am trying to rectify the poor pressure problems we have at the moment as a bungalow. I am sure this will get worse when we add more rooms on the next level and a bathroom?

    I don't understand fully what can be the problem, hence why I want to do my research first before getting a professional in to do the work, and then if it doesn't work, then they don;t turn around and say the pressure issue is something completely different and not related to the boiler!

    What I know,
    We used to live in a house about 2 streets down where we are now. The house had convensional boiler in the garage with cylinder in an airing cupboard and the overflow in the loft. We had 3 bathrooms and a kitchen. We never had the water pressure issue that when one tap is open, then the water pressure dropped. Both cold and hot had good pressures.

    We are now in a bungalow that has a cobi 30Si boiler. It is fitted downstairs ( looks like it used to have conventional somewhere else as in the loft there are lots of pipes that have just been chopped off and left in there when the boiler was replaced ). Cold water pressure is good, but when someone opens a tap in the kitchen, the water pressure drops slightly but not much. But how water is worse. When someone opens tap in the kitchen, the other outlets drop to almost dribble.


    My understanding is that combi heats up water as needed, where as the convensional, heats up the water in the cylinder and it is this cylinder that also heat up the CH water.

    But this is as far as I know and what cause pressure drops is what I don't understand.
     
  6. Naz1977

    Naz1977

    Joined:
    22 Nov 2016
    Messages:
    174
    Thanks Received:
    4
    Country:
    United Kingdom
    By the way, by conventional I mean condensing. But I am sure you understood. :D

    Edit:
    Seems they are not the same! OMG! So many different things. Wish someone could tell me which I need!
     
    Last edited: 17 Jan 2018
  7. bernardgreen

    bernardgreen

    Joined:
    3 Nov 2006
    Messages:
    25,823
    Thanks Received:
    2,571
    Location:
    Bedfordshire
    Country:
    United Kingdom
    Yes, but to get the water heated the boiler has to first heat the metal of the heat exchanger from cold. When the water stops flowing the heat exchanger is still hot. This heat disapates into the atmosphere as the heat exchaber in the boiler cools down and is wasted. This occurs every time hot water is needed.

    With a cylinder the exchangers only cools down once after the water in the cylinder has been heated, less wasted heat.

    In most systems the water flowing through the radiators is heated in the boiler. The same water can flow through a coil in the cylinder to heat the water in the cylinder. The waters do NOT mix, the coil is like a radiator inside the cylinder to heat water.

    There are systems where a cylinder is used as a heat store to supply heat to the radiators.

    Edit quoting error corrected
     
    Last edited: 17 Jan 2018
    • Like Like x 1
  8. Keithmac

    Keithmac

    Joined:
    10 Oct 2017
    Messages:
    2,147
    Thanks Received:
    342
    Country:
    United Kingdom
    I fited a Slamander Homeboost pump before Christmas and it's a godsend (all our street and neighbouring have really poor water pressure).

    Bath takes around 10 minutes to fill now rather than 20 odd!.

    We have a Bosch combi and it's doubled it's output after fitting the Homeboost.

    Maybe check your flow rate per minute on hot and cold and post up what you're getting?.
     
  9. Naz1977

    Naz1977

    Joined:
    22 Nov 2016
    Messages:
    174
    Thanks Received:
    4
    Country:
    United Kingdom
    I have no means of testing the flow rate. Can you get a cheap one from screwfix?
     
  10. Sponsored Links
  11. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    6,370
    Thanks Received:
    883
    Country:
    United Kingdom
    You only need a big bowl/pan or bucket and a clock or watch with a second hand.
    Turn the tap on full and divide the volume by the time to produce it.
    You can use kitchen scales to weigh the water if you don't have graduations on your pan. 1ml is 1g near enough.
     
    • Like Like x 1
  12. Naz1977

    Naz1977

    Joined:
    22 Nov 2016
    Messages:
    174
    Thanks Received:
    4
    Country:
    United Kingdom
    cool. I have plenty of scales in the house.

    So I can open the tap fully, and fill a bucket in lets say 30 second. Weight the water and lets say it is 500g. This means 500ml per 30 seconds, or 1000ml ( 1lt) per minute. Is this correct ?
     
    • Like Like x 1
  13. gasbanni

    gasbanni

    Joined:
    7 Jan 2007
    Messages:
    8,744
    Thanks Received:
    1,025
    Country:
    United Kingdom
    Check the stop taps both in the house and in the street are fully open.
    Your water supply company can check you pressure for free and let you know if it's a problem generally in the are or specific to just you.
    It might be a case of upgrading the supply from the external stop cocktail in to the house, yes it will mean some digging up but it's not as daunting as it sounds the you could have a 25mm mdpe pipe put in and have a great flow and pressure. Getting the water board to check first might prevent a lot of hassle.
     
  14. John D v2.0

    John D v2.0

    Joined:
    26 Aug 2016
    Messages:
    6,370
    Thanks Received:
    883
    Country:
    United Kingdom
    Spot on, although it should be a lot more, expect 8+ litres a minute
     
  15. I'm sure that you have a measuring jug in the kitchen. Measure how long it takes to fill to a litre, and that'll give you litres per minute. If it takes 7 seconds, then that'd be about 8.5 litres per minute.

    You also need to know what the water pressure is like as well, both with all the taps closed, and with one tape running, but if you lived a couple of streets down, and the water pressure was good, then the area should be okay.

    If you're doing an extension, then the builders can dig a trench and drop in a new water pipe dead easily.

    The overflow you refer to, is actually a feed and expansion tank, and with a new boiler, it'll be a pressurised system, so won't need that any longer. Whilst Bernard may be right in saying that a combi is not as efficient on small amounts of water, they are fine in a small property, and compact and convenient, and if you get a combisave fitted, then they'll hold the water back till it's hot, and then allow it to flow - this then makes them more efficient for small volumes.

    But you liked the old boiler and tank that you had, so you've got good experience of it. Get a quote for that when you get the plumbers in.
     
  16. ServiceNumpty

    ServiceNumpty

    Joined:
    9 Sep 2007
    Messages:
    6,962
    Thanks Received:
    1,697
    Location:
    Nottinghamshire
    Country:
    United Kingdom
    Something to bear in mind. As you say you will have a small loft space, and you want to put the cylinder up there, remember the cold water cistern will have to sit above it. And if you wish to use pumped showers you will need a big one.
     
  17. Interesting. Hadn't thought he might be reffering to the cold water cistern when he mentioned the overflow, but this would be got rid of as well in an upgrade. I haven't seen a working cold water tank in use in over 35 years
     
Loading...

Share This Page