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Y-Plan Woes...

Discussion in 'Plumbing and Central Heating' started by X6tus, 29 Sep 2018.

  1. X6tus


    28 Sep 2018
    Thanks Received:
    United Kingdom
    Hi all, I'm looking for some help as I've exhausted all my resources and knowledge. Let me describe the current system...

    Boiler: Potterton Suprima 30
    Timer: Center EHE0200160
    Frost-Stat: Potterton PRT-100
    Room-Stat: Potterton PR-100
    Hot Water Cylinder: Joule Cyclone Indirect/Un-vented
    Cylinder Stat: Joule Cyclone Dual Thermostat
    Configuration: Y-Plan

    Mechanical Configuration: https://s3.eu-west-2.amazonaws.com/prime23.uk/mech.png
    Electrical Configuration: https://s3.eu-west-2.amazonaws.com/prime23.uk/elec.png

    Ok, so I've just added the Joule Indirect cylinder into the system as per the mechanical diagram above. The electrical configuration is also as per the diagram EXCEPT that the pump live is wired to a separate Pump Live (instead of the switched live) from the boiler to allow it to overrun.

    Setting the timer H/W ON (continuous), C/H OFF, cylinder stat to 50 deg, the pump runs, the boiler fires up, the valves are correctly positioned and heat flows to the cylinder only. The system correctly shuts everything down when the cylinder stat temperature is reached.

    Setting the timer H/W OFF, C/H ON (continuous), room stat to 30 deg (max), the pump runs, the boiler fires up, the valves are correctly positioned and heat flows the the radiators only. The system correctly shuts everything down when the room stat temperature is reached.

    So my problem..

    Setting the timer H/W ON (continuous), C/H ON (continuous), room stat to 30 deg (max), cylinder stat to 50 deg, the valves are correctly positioned and heat flows to both the cylinder and the radiators as expected. All good so far!

    Now when the cylinder stat reaches the required temperature the system shuts down completely (boiler off, pump off after a bit of overrun). It does not divert the heat from the boiler to the radiators as I would expect. At first I thought it was just the room stat already at the required temperature but I have tested with setting the room stat to minimum so the radiators/house is cold and let the cylinder heat up and shutdown, then turn up the room stat back up to maximum. I would expect the system to fire up to satisfy the room stat requirement but it does not.

    I've double, triple checked all connections and valves. All are working correctly and is proven when the heating and hot water settings are used separately on the timer. It's just that when both are used together the cylinder stat seems to take control and the system shuts down when it is satisfied and it ignores the room stats requirements.

    Has anyone else seen this or can explain what might be happening?

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  3. flameport


    10 Mar 2007
    Thanks Received:
    Poole, Dorset
    United Kingdom
    Cylinder stat has no HW Off connection which is required for Y plan systems.
  4. Elkato531


    22 Jul 2009
    Thanks Received:
    United Kingdom
    Never understood why people use a Y-plan for unventeds. They supply a zone valve in the kit so just add another and use an S-plan setup. Electrically less problematic.
    Assuming you have G3 qualification of course. If not, leave well alone.
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    3 Sep 2019
    United Kingdom

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