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Discuss will i loose hot water pressure with a system boiler in the Central Heating Forum area at

  1. Graham SW

    Graham SW New Member

    I only have a 15mm pipe from the water main and have been told this may be limiting if i go for a system boiler as some of the water pressure is used to fill the tank while the hot water is being used. Is this correct and would a combi boiler with a high flow rate be better?
  2. gingalig

    gingalig GSR

    Ideally you would need a dedicated 22mm supply to an unvented cylinder and then balance the supply via the inlet set, although you can use an accumulator of the correct size if you have the space to help balance any pressure loss. You could consider a 111w viessman or 200 series combi storage boiler, but what ever you choose you would need to know the flow rate and water pressure before you could make any decision. To fit an unvented you would need to be or have a plumber that is G3 registered.
  3. Last Plumber

    Last Plumber Trusted Plumber GSR

    You need to know the Pressure and flow rate at the first draw off point on the main really. That will help a lot.
    I have installed many Unvented Cylinders off a 15mm main. However, I have upgraded all of them to 22mm pipe from the entry point of the main over to the cylinder. In some cases the external supply needs upgrading and of course some areas have poor water pressure and flow either due to elevation, mains size or demand.
    • Like Like x 1
  4. SimonG

    SimonG Trusted Plumber

    Check static and dynamic pressures. That is with outlets closed and a tap open.
  5. fixitflav

    fixitflav Active Member

    Is it an unvented HW cylinder, or conventional type fed from the CW storage tank?
  6. Riley

    Riley S. Mod Trusted Plumber GSR Top Contributor!!

    Yes what has been specced to work with your system boiler
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