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Downstairs heating turning itself on, upstairs fine?

Discussion in 'Plumbing and Central Heating' started by b0ng0, 9 Feb 2021.

  1. b0ng0

    b0ng0

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    Problem:
    • Downstairs radiators keep coming on by themselves, even when thermostat/programmer would indicate CH either shouldn't be on at current temp/time or programmer is deactivated but CH still comes on.
    • Upstairs rads function at the correct time/temp as per the programmer.
    Tried so far...
    • I have switched the programmers around (up and downstairs, the display part of the body which contains the batteries is removable) but this does not solve the problem, downstairs still randomly comes on.
    • CH downstairs randomly comes on when the hot water programmer is off, which makes me think it's not the diverter valve stuck in position.
    • I can get the downstairs radiators to turn off by forcing the programmer to click on (audible click) then press deactivate, but if I leave it deactivated eventually it will turn on again by itself. Again, upstairs functions normally.

    Plumbing Setup:

    • Boiler: Potterton Promax SL (frost stat in garage along with boiler)
    • HW Tank: Santon Premier Plus
    • Zone 1 (Downstairs) Diverter Valve: Honeywell 2 Port set to Auto
    • Zone 2 (Upstairs) Diverter Valve: Bosstherm 2 Port set to Auto
    • Thermostat/Programmers: Myson MPRT hard wired (one upstairs one downstairs, fresh batteries and have been reset).
    I'm a bit stumped at this point - any help is very welcome! Some pics below if that helps...

    Myson Programmer and Backplate
    myson_prog.PNG
    myson_backplate.PNG
    CH Layout
    ch_layout.PNG
     

    Attached Files:

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  3. cross thread

    cross thread

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    Maybe the frost stat is linked to the downstairs zone valve
     
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  4. ianmcd

    ianmcd

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    downstairs zone valve is sticking
     
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  5. b0ng0

    b0ng0

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    I suppose it could be, any way to troubleshoot this to see if it really is causing the issue?
     
  6. b0ng0

    b0ng0

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    I'm completely ignorant when it comes to these valves, should I move the arm to MAN and then back again a few times? Is there anything else that I could do to prove this is the issue as I would probably have to get a plumber in to replace it if that's the case.

    Also, I can deactivate the heating for a few hours to the point where the rads are cold and leave the programmer off but it still comes on - doesn't that suggest that the diverter valve is fine but something is triggering it to open up specifically for heating?
     
  7. ianmcd

    ianmcd

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    The lever that you refer to is simply for filling the system, with both zones switched off, when you try to move the lever across you should feel resistance, with both up and down calling for heat the lever should slide with no resistance as the valve is open, switch the d/stairs off and see if the valve lever is floppy , if it is it has seized
     
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  8. cross thread

    cross thread

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    The frost stat is adjustable, it would be set at around 5 degrees.
    Are the rads only coming on when it’s cold
     
  9. b0ng0

    b0ng0

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    The frost stat is set to the minimum temperature (and has been since the house was built 5 years ago so nothing has changed there). It's obviously very cold right now so it could be triggering the frost stat, but should that connect to the radiators? I've no idea how to check.
     
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  11. ianmcd

    ianmcd

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    what was the result when you checked the valves
     
  12. Jajodu

    Jajodu

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    Suspect valve no 8 in your schematic, sticking on and firing up the boiler.
     
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  13. b0ng0

    b0ng0

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    Not checked yet, system and pump is running so don't want to manually open the valve while the pump is running. Will report back when the current cycle turns off (it's going to be a cold one tonight so at least need to heat the house up before I play with valves!).

    Additionally I waited till the rads downstairs went cold and just removed the programmer from the wall and so far they have stayed cold all afternoon. Bit of a crude stop gap at least.
     
  14. ianmcd

    ianmcd

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    wont make the slightest bit of difference
     
  15. b0ng0

    b0ng0

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    I tried moving the leaver when all zones were off and felt steady resistance (and some small noise which I assume is the port opening). When I let go it moved back into the auto position. I moved the other leavers to compare and they all had the same feeling of resistance.

    None of them really felt loose or flappy.
     
  16. Jajodu

    Jajodu

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    There's an internal microswitch that fires up the boiler, that needs checking. Do you have a multimeter?
     
  17. b0ng0

    b0ng0

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    I do, where would the microswitch be located?
     
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