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Twin peller pump on combi boiler

  • 21-12-2015 11:48am
    #1
    v638sg7k1a92bx
    Closed Accounts Posts: 2,913 ✭✭✭


    Anyone know if it's possible to fit a twin peller pump on a combi boiler to pressurise the who domestic supply. I understand that a single peller pump is preferred to avoid the risk of a dry run on the boiler but can I install the twin peller without having to put in a water tank and have it connected directly off the boiler?


Comments

  • #2
    Pete67
    Registered Users, Registered Users 2 Posts: 1,257 ✭✭✭Pete67


    No, the combi boiler needs to be supplied either with mains water, or from a single impeller pump fed from a break tank. In either case, both hot and cold supplies to the premises should come from the same source. (mains or boosted supply via a break tank and pump set). This ensures that mixing valves have equal inlet pressure on the hot and cold sides, and can operate correctly.

    If the mains supply pressure is not adequate then you need a break tank feeding a booster pump which then provides pressurised cold water the domestic premises and also to the combi boiler inlet. You cannot connect a pressure boosting pump directly to the mains water supply, even if it is on the outlet side of the combi boiler.


  • #3
    v638sg7k1a92bx
    Closed Accounts Posts: 2,913 ✭✭✭v638sg7k1a92bx


    Pete67 wrote: »
    No, the combi boiler needs to be supplied either with mains water, or from a single impeller pump fed from a break tank. In either case, both hot and cold supplies to the premises should come from the same source. (mains or boosted supply via a break tank and pump set). This ensures that mixing valves have equal inlet pressure on the hot and cold sides, and can operate correctly.

    If the mains supply pressure is not adequate then you need a break tank feeding a booster pump which then provides pressurised cold water the domestic premises and also to the combi boiler inlet. You cannot connect a pressure boosting pump directly to the mains water supply, even if it is on the outlet side of the combi boiler.

    Sorry not to the mains.

    What I mean is: mains to the combi boiler, combi boiler to pump which pressurises the domestic supply only and not the rads, heating etc?

    Can the pump be a twin peller or do I have to use a single impeller pump?


  • #4
    Pete67
    Registered Users, Registered Users 2 Posts: 1,257 ✭✭✭Pete67


    Sorry, but no. You cannot connect the DHW outlet of a combi boiler to a pump where the boiler is supplied from the mains, this is the same as pumping the mains directly. It does not matter whether it is a single or twin impeller. The correct way to boost the pressure is to make use of a break tank feeding a booster pump set which then supplies the combi and also the cold water distribution. Make sure the break tank is large enough to cater for peak demand, as you will likely be consuming water at a far greater rate than the mains can refill the tank.


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