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Combi boiler and cold water tank

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  • 18-08-2022 1:59am
    #1
    CitizenWatt
    Registered Users Posts: 4 ✭


    Getting a new combi boiler for a single bathroom and kitchen setup.. the plumber wants to use the cold water tank for cold and mains for the hot water.. should the pipe from the cold water tank to now defunct hot water tank be just capped or removed?



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    #2
    Sleeper12
    Registered Users Posts: 16,928 ✭✭✭✭Sleeper12


    So many threads where this comes up. Best practice is cold going to taps & cold going to the combi comes from the cold water tank & both are pumped. This way you get equal pressure on the hot & cold taps. Most thermostatic showers will no longer function correctly with hot pressurized coming from the mains & the cold coming from the tank without being pumped.

    Running a combi directly from the mains supply in Ireland is against building regulations, Irish water by laws & local bylaws.

    From your plumbers point of view, he was probably the cheapest quote & he doesn't have a pump built into his quote



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    #3
    standardg60
    Registered Users Posts: 4,374 ✭✭✭standardg60


    Surely with that setup on a mixer tap the hot would just flow up the tank fed cold.



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    #4
    John.G
    Registered Users Posts: 3,474 ✭✭✭John.G


    Irrespective of the laws, you cannot mix mains mains hot (or cold) with gravity cold (or hot) as the mixing will only take place at the lower pressure, ie if you had a shower flow of say 10LPM from equal hot&cold pressures of 2bar you will only get ~ 5LPM if cold is gravity fed even if the shower is downstairs and more like 3.5 to 4LPM upstairs as the downstairs gravity head will be ~ 0.5bar and the upstairs only ~ 0.25bar and flow is proportional to the sq.root of pressure.



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