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Drayton ZA5 actuator head alternative

Discussion in 'Plumbing and Central Heating' started by nickrw, 8 Feb 2019.

  1. nickrw

    nickrw

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    I've had one of my two Drayton Za5 valves micro switches stick on me yet again, this time resulting in the HW permanently stuck on. I'm pretty sure it's this because if I hit it with a hammer it goes off for a while! And I have 4 of these over the years fail with similar faults.

    My question is can the actuator be replaced with a different more reliable model without changing the valve itself?

    I know it's not expensive or difficult to swap the head but I'm tired of repeatedly swapping these every couple of years!
     
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  3. ollski

    ollski

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    No. Sorry. Honeywell is a better lasting valve but you need to replace complete.
     
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  4. nickrw

    nickrw

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    Thanks Ollski for your super quick reply.
     
  5. Gasguru

    Gasguru

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    Quite often you'll find one of the spring lugs has broken off and a single spring is insufficient to return the motor to the closed position.
    With careful disassembling and fettling you can re-attach the spring by hooking it through the baseplate hole.
     
  6. Harry Bloomfield

    Harry Bloomfield

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    The devil himself designed the spring return valve actuators, to give repair work to heating engineers. If you are replacing look at the possibility of installing momo actuators, no springs involved and no highly stressed mechanical components, designed to jam or break. The motor to position and motor back.

    I like you, had constant issues with a spring actuator for decades, but a 3-port.
     
  7. ianmcd

    ianmcd

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    If you have an unvented HW Cylinder you cant use a MOMO valve
     
  8. bernardgreen

    bernardgreen

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    Is there a logical reason for that ?

    Can a MoMo actuator be used in a system with a vented cylinder ?
     
  9. Harry Bloomfield

    Harry Bloomfield

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    I would be interested in the answer too please, but I don't think the OP indicated unvented.
     
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  11. oldbuffer

    oldbuffer

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    Because a MOMO doesn't automatically fail to closed.
     
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  12. ianmcd

    ianmcd

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    as @oldbuffer correctly says , a MOMO does not fail to closed and protect the cylinder, and before you say it , we dont make the rules and yes a spring return can do the same but we have to follow the regulations regardless of whether we agree with them
     
  13. bernardgreen

    bernardgreen

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    A spring return valve can also fail to close when power is removed if the spring cannot drive the motor backwards. The gear ratio between valve shaft and motor shaft is high so a minute amount of resistance to turning in the motor requires a lot of force from the spring.

    Protect from what ? Overheating should be prevented by thermostats acting directly to the boiler. If the MoMo does not close because the power has failed then the boiler will also have lost power and shut down.



    Do you not have an interest in why the regulation are written the way they are.

    Do regulation permit MoMo valves on vented systems ?


    Yes I know in some systems the boiler is controlled by a micro switch in the valve actuator(s) indicating that a valve is open and heat is needed.
     
  14. ianmcd

    ianmcd

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    Why can you not be told Benny Boy, as I already said I do not make the regulations , but as G3 qualified I have to adhere to them , and that is what the regulation states
     
  15. ollski

    ollski

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    This is true, it’s the reason the annual service on the unvented cylinder has one of the checks dedicated to manually making and releasing the spring return valve to ensure it does
     
  16. Harry Bloomfield

    Harry Bloomfield

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    In my small sample of looking after my own heating system, spring return actuators jam open often - Which was the reason I swapped my actuator for a momo, to improve the reliability.

    You mentioned that if the momo lost power, then also would the boiler - that is only true sometimes, but it cannot be guaranteed. There are other possible reasons for loss of supply to the momo as well as potential for internal failures of the momo.
     
  17. Harry Bloomfield

    Harry Bloomfield

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    Yet it is perfectly possible for a spring return to fail on any of the other 364 days of the year. My own heating system would sometimes need a replacement spring return actuator every 18 months. Reliability was so very poor, I would keep a new actuator ready to just pop in. By far the most failure prone part of my entire system - which is why I have now switched it over to a momo. Yes, I do keep a second momo to hand, ready to install, but so far I have not needed to make use of the spare momo.
     
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