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Discuss two central heating pumps in the Central Heating Forum area at

  1. Inverness

    Inverness Plumber GSR

    what setting should the pumps be if they are working together? O/v One on the flow is set 3 and the return pump is at speed set 2. Should the pumps not be set at the speed together?
    Since it's a 3 storey house I've heard about theses loss of head pumps?someone shine light on this please.
  2. king of pipes

    king of pipes Trusted Plumber GSR

    Post some pictures up we may be able to advise you better its not the normal to have 2 pumps on the same circuit unless its under floor heating , low loss header or similar cheers kop
  3. townfanjon

    townfanjon Trusted Plumber GSR

    Guessing sombody may have installed another one to get round a problem
    • Agree Agree x 1
  4. deg

    deg Member

    4 pipe system with a pump for hot water?
  5. Inverness

    Inverness Plumber GSR

    Maybe the reason as the pump can only pump 5 meters max when the house is height is far greater at the top?
  6. doitmyself

    doitmyself Well-Known Member

    The height of the house is not relevant - unless it's more than 15 floors high.
    • Agree Agree x 1
  7. Best

    Best Trusted Plumber

    It does actually matter - a system that has to pump more than 5 metres high needs a higher head pump.
    Or if it has a bigger output needed or has restrictive pipes or radiators, then it also needs higher head pump, regardless of actual height of head.
    The higher head pumps have more torque
    • Agree Agree x 3
  8. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    15 x 2.4 = 36m a 6m head pump isnt going to touch that so it is important
    • Agree Agree x 3
    • Like Like x 2
  9. Chuck

    Chuck Active Member

    Only relevant if the pump is for filling a tank from a well, or similar, but I doubt this is the case here.

    Assuming, what is being described are pumps that circulate water around a closed loop, i.e. a conventional CH system, the vertical height doesn't matter. What matters is that the pump is correctly sized for the impedance of the circulating loop, which depends on the usual things (diameters, lengths, bends, etc.) and the impedance is low enough for a standard pump (ca 0.5 bar head) to achieve a sufficient flow rate.

    Most likely reason for two pumps is one for heating and one for hot water. It's possible that someone has put two pumps in series because the circulation rate was limited by flow impedance but I wouldn't consider it to be good practice. The right solution IMO is cleaning blocked pipework or replacement of undersized section(s).

    • Agree Agree x 1
  10. doitmyself

    doitmyself Well-Known Member

    I can understand the average house owner thinking that the head of a circulator relates to how high, vertically, it can pump water. But I am completely at a loss when I read trained plumbers and heating engineers saying exactly the same thing. It makes me wonder if those responsible for their training suffer the same delusion.

    It might cause less confusion if the head was always expressed in bar or kilopascals; "metres head" should be consigned to the same dustbin as BTU.

    The 15 floors I mentioned earlier is related to the maximum permitted static pressure of a system.
  11. Best

    Best Trusted Plumber

    Then what does metres head of a pump indicate? And why do many small system boilers come with 6 metre pumps? A 5 metre pump will not pump well on a 3 story building.
    • Agree Agree x 1
  12. doitmyself

    doitmyself Well-Known Member

    Metres head is one way of measuring the pressure the pump is able to produce. It could also be measured in Bar or Kilopascals.

    If you connect a U-gauge manometer to the output of a circulator this will show the pressure produced. Just like measuring the pressure of a gas supply.

    The reason for installing 6m pumps in many system boilers is that modern heat-exchangers have such a high resistance that a 5m pump would have very little pressure left to circulate water through the rads.

    The pipes for a 3 storey building will be longer than for a 2 storey so the pressure loss will be greater, which will require a pump with a higher head.
    • Like Like x 1
  13. Chuck

    Chuck Active Member

    It refers to the pressure difference (6m H2O, i.e. 0.6 bar or 60kPa) between the pump inlet and outlet at which the flow-rate (e.g. in m^3/hour) has fallen to zero. You can see for yourself by looking at the 'pump-curves' published by the manufacturers. For example: datasheet 1214.pdf

    It's not always true that 'A 5 metre pump will not pump well on a 3 story building'. When it is true it's because the pipework / radiator / pump sizing has been got wrong.
    • Like Like x 1
    • Agree Agree x 1
  14. Best

    Best Trusted Plumber

    Thanks for both explanations.
    I understand the 6m pumps were thought to be needed for modern heat exchangers. I also know the head of a pump can be thought of as the resistance.
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