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Combi boiler supplied from the cold water tank

  • 06-04-2024 9:51pm
    Registered Users Posts: 45


    Need some advice on a combi boiler setup, also, Im interested to gain some insight on how the system works to be honest (nerd at heart). I have a combi boiler but I only use it to heat my hot water cylinder and radiators.

    Im doing some renivations and it was suggested that I can get rid of my hot water cylinder and get my hot water supplied from the combi boiler. As the combi boiler has a heat exchanger to heat the radiator water and a secondary heat exchanger that can be used to supply instand hot water.

    My fear is that this setup could resilt in a drop of hot water pressure as the combi boliler will can its input from the mains. Would or could the combi boiler get its input water from the cold water tank in the attic ? Or is this normal ? Does it have to be mains fed ?



  • Registered Users Posts: 1,371 ✭✭✭Lenar3556

    If you are planning to remove the cylinder, you need to ensure that the combi boiler will be in a position to meet the hot water demand without the benefit of a cylinder acting as a buffer. It would be good to understand why the cylinder was installed in the first instance. Do you have high performance showers? Is there any secondary heat sources which heat the cylinder? For example stove or solar panels. Is there a pressing need to remove the cylinder?

    Once that is understood and if you decide to proceed, the best job is to feed the combi from the attic storage tank with the benefit of a pump to increase the pressure to the boiler to circa 2 bar. This arrangement is preferable to feeding the boiler directly from the mains as it provides water at a consistent volume and pressure. You also have a store of water in the event of a mains outage.

  • Registered Users Posts: 45 VidaLoca

    Does my cold water tank need to be increased in size ? Or, what size is good enough ?

  • Registered Users Posts: 1,371 ✭✭✭Lenar3556

    Not necessarily. Although you might decide to add additional capacity depending on the current size and demands. A second tank may be an option alongside the current one.

  • Registered Users Posts: 5 thepressurehub

    google Irish Water Code of practice, Scroll to page 93 for Irish water storage regulations, and see what you have in place capacity wise.

  • Registered Users Posts: 16,958 ✭✭✭✭Sleeper12

    It's against the building regulations to connect a combi boiler to the mains water supply in Ireland. Best practice is to feed the combi from the cold water tank in the attic. The hot & cold should be pumped coming from the attic tank. Most thermostatic showers can't run correctly with different pressure on the hot & cold side.

    You need to be careful if you have a power shower like a Mira Event, Triton Novel SR, Aqualisa Aquastream. These can't be connected to the mains water supply and they can't be connected to a pump.

    Personally I'd leave well enough alone & keep the system you have.

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