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Discuss Three Port Valve Puzzle in the Central Heating Forum area at

  1. Jock Spanners

    Jock Spanners Plumber GSR

    Evening All,

    I changed a Drayton three port valve today as the valve was completely seized. It appears to be wired correctly. When I switch to HW it moves to HW and when I switch to Mid it moves to Mid. But when I switch to Heating it clicks repeatedly, the small lever on the actuator stays in the Mid position and the boiler stays off. Has anyone any idea what's wrong?


  2. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    Faulty valve head/wiring? Or what boiler is it on? Is it a Vaillant open vent?
  3. Jock Spanners

    Jock Spanners Plumber GSR

    It's an old Myson. My customer now informs me he had to turn the cylinderstat up to get the heating to come on.
    • Funny Funny x 1
  4. Harvest Fields

    Harvest Fields Trusted Plumber GSR Top Contributor!!

    Remove the wiring and do it again at the junction box mate.(Properly) I wouldn’t trust any of the wiring now.
  5. king of pipes

    king of pipes Trusted Plumber GSR Top Contributor!!

    Its obviously wired incorrectly Jock 3ports are notorious for back feeds and trouble some operation , better to convert to a s plan. Cheers kop
    • Agree Agree x 1
  6. fixitflav

    fixitflav Member

    I suppose the old valve was also a mid-position type like the new one (not an older either/or Honeywell system W type)? If so it sounds like the old valve was stuck in mid-position so turning up the cylinder stat to get the boiler running also heated the rads. And the wiring was faulty.
    I would check all the wiring is in line with Drayton's diagram, rather than wiring the new one the same, if that's what you did. You could also check the voltages from the stats are whsat they should be in various conditions.
  7. fixitflav

    fixitflav Member

    Don't know whether you've cracked this yet, but I dug out some data and wiring diagrams for system with mid-position valve which might help. Shows how it's meant to work!
    I tried to "Upload a File" using button below, but nothing seemed to happen, so I pasted it into the message. But some uploads seem to have been added. I'm new to this forum!

    Electrical signal

    Valve position

    No power to valve

    Hot Water only (open to Port B only)

    240V on white wire

    Hot Water & Heating (open to Port A & B)

    240V on white & grey wire

    Heating only (open to Port A only)

    240V on grey wire only

    Valve is held in last port of call

    Please Note:

    The Manual Lever on the side of the valve, is to allow the system to be filled, it is NOT a position indicator.

    If the system is powered the valve will remain in the last port of call, either open to Port A or open to Port B. It will only move when there is a further call for Heating or Hot Water.

    Electrical Operation

    In the Y Plan system, when Hot Water is called for, power to the boiler is provided directly from the cylinder thermostat, the valve is not energised. When Heating is also called for, the Heating ON wire (white) is energised and the valve will motor to and stop in a mid-position.

    If the Hot Water is then satisfied, (either by the programmer or cylinder thermostat) the Hot Water OFF wire (grey) is energised. Because there is still a demand for Heating the valve will then motor towards the Heating Only position and switch a 240V supply onto the boiler. The orange wire only has a 240V supply from the valve when there is a call for Heat in the Heating only position i.e. 240V on white & grey wires.

    When this Heating demand is satisfied, during a Heating ON period, 50V to 150V (voltage can vary according to the supply) will remain on the orange wire and the valve will continue to be energised and warm to the touch. Switching Hot Water ON or turning OFF at the mains will de-energise the valve and it will spring return back to the Hot Water only position until the next demand.
    • Like Like x 1
  8. DevsAd

    DevsAd Member

    I understand that, certainly with the common Honeywell V4073A 3-porter, it defaults to the DHW position if there's no power - ie the spring will return it to that position.

    If your Drayton is the same, and you turned on the power after replacing it and then switched for HW, the motor shouldn't have moved at all as it should already have been in the 'correct' position. So - again, if it's the same - the fact that it moved when power was restored and HW called for suggests it was incorrectly wired.

    But that's a guess...
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  1. should a honeywell three port valve remain energised

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