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Discuss Mid-position valve issues in the Central Heating Forum area at

  1. Andy C

    Andy C New Member

    I'm having an odd issue with my mid-position valve. This is a bit lengthy as I want explain the steps I've taken...

    I have a y-plan heating system, with a 3-way mid-position valve next to my HW cylinder.

    My hot water is working fine, and when there is both water and heating demand, the radiators get warm.

    If there is only heating demand, the mid-position actuator makes a clicking sound, you can see it trying (and failing) to move to the heating only position, and the primary pump does not start.

    I've made a video of this if you want to see (the volume needs to be pretty hear the clicking):

    I replaced the actuator, and the first time it went all the way to heating (and the pump started), then on the second attempt got stuck in the mid-position again, with the same clicking.

    I had a plumber round and he replaced the valve body.

    Same issue.

    I thought I'd try draining the system, filling with cleaner and replacing the actuator head again, just in case it have been damaged whilst on the old valve.

    I did that, but this time I did not put the (new) actuator back on the valve, started the system on heating only.

    The unmounted actuator moved all the way across to the H position. All good.

    I add HW by turning it on at the programmer and adjusting the cyl. stat, and the actuator moves to the M position. Also good.

    Now, if I turn off the HW (by reducing the stat setting on the cyl.), presto: The actuator get's 'stuck' in that clicking mode trying to move to H.

    This actuator has never been on the body!!

    Even more interestingly. If I start it CH only, the actuator moves across. If I then turn off CH demand from the stat, the boiler keeps running and the head stays in H.

    This seems electrics related? Could the control unit (Sunvic SP50) be the issue?

    I'm not really sure where to go next... any advice would be gratefully received.
  2. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    have you got a multi meter?
  3. Vee

    Vee Plumber GSR

    Your replacement actuator doesn't look new, as the position indicator in not visible?? Could be the off switch from programmer or cylinder stat. Check 240V returning on grey.
  4. Andy C

    Andy C New Member

    Yes, but not used it in many years...
  5. Andy C

    Andy C New Member

    That is a video of the old actuator. The new one has exactly the same symptoms.

    That's interesting. My cylinder stat was replaced not long back. Could you give me a little more detail on how to check it?
  6. ShaunCorbs

    ShaunCorbs S. Mod Trusted Plumber GSR Top Contributor!!

    when the valve/ head is going back and to what wire has voltage on them minus the blue and green
  7. Andy C

    Andy C New Member


    Ok, it's been a while, but when there is no demand, I get 240v between the earth and:
    1. The double yellow coming in from the top.
    2. The black coming in from the bottom (left of the grey/light blue wires)
    When the clicking is happening I get 240v between:
    1. The double yellow coming in from the top.
    2. The red from the top, white from the bottom.
    3. The black coming in from the bottom (left of the grey/light blue wires)
    I also get a fluctuation between 2V and 7V on:
    1. The grey/light blue
    2. The red/brown from the bottom next to those
    3. The brown only from the bottom.
    Is this useful?
  8. Vee

    Vee Plumber GSR

    Looks as though there is no off signal. Take the blue and red from the terminal with the grey. Check 240V on their own to check off signal. Looks like blue is off signal from cylinder stat when CH & HW on together. Red CH off from programmer. Blue (if its cylinder stat off, should be 240V when cylinder demand satisfied and call for CH. Hope its as I see it, bit off guess work.
  9. Andy C

    Andy C New Member

    I was starting to try and figure out what was going wrong via the multimeter, and I think I noticed a wiring issue. According to the Drayton documentation, the orange wire should go to the 'calling' on the cyl. stat:


    Calling on the stat is position 1:
    1 is the black cable, 2 the light blue cable:

    Looking at my wiring, the orange is actually incorrectly wired up to the common live from the stat:
    Am I reading this right? The orange cable at position 1 should actually be at position 2??
  10. Vee

    Vee Plumber GSR

    I would try it by swopping the black (call, 1) with the brown (Common, C) from the cylinder stat, without moving the orange.
    • Agree Agree x 1
  11. Colin0368

    Colin0368 New Member

    Is it wired for hot water priority ?
  12. Andy C

    Andy C New Member

    That has done the trick! Switched those two wires over and everything appears to be working properly!

    Thanks Vee!!
  13. Andy C

    Andy C New Member

    I don't believe so. If both are demanded, the valve is set to the mid position.
    • Like Like x 1
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