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Discuss 3 port valve fitted wrong way around in the Central Heating Forum area at

  1. Markbro

    Markbro New Member

    Hi ..quick question .
    If mid position valve is fitted the wrong way around ..would swapping stats wireing around sort it out .?
  2. Ric2013

    Ric2013 Plumber

    About to go to bed, so half asleep. IIRC, the way a 3PV is wired won't allow that as not quite as simple on the wiring side as you might expect. Think there's a DHW call for heat and a DHW satisfied cable core, but not the same for CH.

    It's a bad idea because if you have it plumbed backwards it will be held by the motor permanently into the CH position (the one you'd be using for DHW) from April to September and probably will not last as long as it should, and waste electricity.

    That said, if you are happy re-wiring your CH room stat too, then it might work if your room stat has a terminal that becomes live when the stat is satisfied. Not all stats have this terminal.

    I wouldn't bother going to all this effort to do it wrong myself.
  3. Markbro

    Markbro New Member

    Oh eck....looks like draining the system again then....thanks for reply
  4. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    No you can't need to swap the body
    • Agree Agree x 1
  5. doitmyself

    doitmyself Well-Known Member

    Are you sure it's a mid-position, not a diverter valve (two positions only, CH or HW, no mid-position, CH and HW)?
  6. Ric2013

    Ric2013 Plumber

    Quite rare these days?
  7. doitmyself

    doitmyself Well-Known Member

    Diverter valves are frequently used on systems with Weather Compensation or Opentherm as the flow temperature can be much lower when CH is called. A mid-position valve is unsuitable in these situations.

    The diverter valve may be installed back-to-front with port A connected to the HW cylinder and Port B to the CH. This means that the valve is only powered when HW is called.
    • Like Like x 1
    • Informative Informative x 1
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