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nest with 3 port valve

Discussion in 'Plumbing and Central Heating' started by Jonrajesh, 4 Dec 2016.

  1. Jonrajesh

    Jonrajesh

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    Hello All,

    I need a bit like guidance on how the nest should work on a Y-Plan setup. Had mine fitted by a certified nest installer. However for getting any real heating through the radiators I need to switch on the Water Heating as well, which is a bit strange. Also the rest position of the 3 port is at CH now (with CH & HW off) which again is not per documentation that I have come across.

    Can anyone who has a similar setup please tell me if this is the way it should be or the wiring probably is completely messed up while installing the nest?

    Cheers, John
     
  2. jackthom

    jackthom

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    It is normal for the valve to sometimes end up in the heating only position even when there is no longer any demand for heat. The hot water off signal will hold it there until such time as there is demand for hot water.

    When you have hot water off and heating on does the boiler fire up at all?

    If it doesn't there could be a wire from the valve misconnected or the valve micro switch could be faulty. Some pictures of the wiring centre would be useful.
     
    Last edited: 4 Dec 2016
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  4. Jonrajesh

    Jonrajesh

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    @jackthom
    Thanks for the reply. The boiler is firing in all required positions and the actuator is also moving as per the call made. But when it is only on CH the boiler keeps shutting down and radiators never reach the required temperature

    Again I don't think it is any airlock in the system as I removed the actuator in the CH + HW position and just tried CH alone and it is the same behaviour (keeps shutting down and pump keeps running thus cooling the radiators)

    That is why I am thinking if it is wired incorrectly.
    I am planning to trace the wires this week to understand how the call for each is being made and what is going through my circuit. Hence the question what should be the rest position. ( when there is no voltage on any wires - main power cut,then the rest position is HW)
     
  5. jackthom

    jackthom

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    When the boiler is about to shut itself down in heating only mode can you compare by hand the difference in temperatures between the boiler feed and return pipes. If circulation through the central heating system is poor the return will be cool, even when the feed is at max temperature.
    The problem may be a combination of restricted flow and long periods when the boiler is inhibited from restarting i.e. in anti cycling mode.
     
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