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Discuss Suitable Pump Replacement in the Central Heating Forum area at

  1. Berksguy

    Berksguy New Member

    Thanks for your detailed reply. Currently the bypass in my heating system is via a towel radiator in a bathroom. Do you think it would be best to keep it this way or move to the auto bypass and setter solution?
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    depends if you go fixed speed adjustable pump then have a separate bypass fitted if you go for a load adjustable pump then no need
  3. doitmyself

    doitmyself Well-Known Member

    What makes you think the towel rad is a bypass?

    There are only two reasons for a bypass:

    1. The boiler manufacturer says it is necessary;
    2. To provide a path when all motorized valves are closed and the boiler has pump overrun.

    You haven't said which boiler you have or anything about your system, so I don't know which applies.
  4. Berksguy

    Berksguy New Member

    When the boiler was originally installed the plumber told me to never turn off the one towel radiator as it was the bypass for the boiler.

    The boiler is a Potterton Suprima 120L.

  5. doitmyself

    doitmyself Well-Known Member

    The Suprima 120L has pump overrun. The MI's suggest either an auto bypass valve or a bathroom rad/towel rail to give the required circulation when motorized valves are closed. In either case, it has to be connected to the flow between the pump and the MV. If the towel rail solution is used there is a permanent flow through the rail, even when towels don't need to be heated. Replacing the towel rail with an auto bypass would be better; but then there's the problem of heating the towel rail. It would need connecting to either the CH or HW flow after the motorized valve(s).

    I have assumed that you have two motorized valves. If you have only one mid-position valve (3 pipes connected), you don't really need a bypass as one port is always open.

    The MI's also say that a large domestic/small commercial pump is required due to the high flow rate and large pressure drop through the heat exchanger. The UPS2 25-80 is not ideal, but it will work.
  6. Berksguy

    Berksguy New Member

    Thanks again for your detailed responses.

    There are two separate motorised valves in my system. The towel rads coming on when the hot water is being heated is usually a good thing. However, on the few summer days where we get high temperatures, it would be useful to be able to turn off the radiator.

    What would you suggest as an alternative to the UPS2 25-80?

  7. doitmyself

    doitmyself Well-Known Member

    So you will need an auto bypass to take the place of the towel rad, which will need its flow moved from after the pump to after the HW valve.

    The 25-80 will be fine. It's just that the pump will not be working at the optimum point on its flow/head curve, so running costs will be slightly higher.
  8. Berksguy

    Berksguy New Member

    I arranged for a heating engineer to call around yesterday to have an initial look at the work I need undertaking. He didn't turn up and when I rang him he provided a feeble excuse for not coming. So I'm still looking for a good heating engineer that carries out work in the Reading area.
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