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Nest 3rd Gen and Worcester Bosch 8000 Problem

Discussion in 'Plumbing and Central Heating' started by Muj, 5 May 2021.

  1. Muj

    Muj

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    Hi guys,

    I seem to have a somewhat weird problem.

    I’ve recently had a new radiator system along with a new boiler and Nest thermostat installed.

    The problem is quite a weird one so I’ll explain the best I can.

    The thermostat is in my hallway and my house is 2 floors. Lets assume the ambient temp is 17°, I then crank up my thermostat to 30° which then fires up the boiler and rads start getting hot.

    My problem starts here, let’s say the thermostat goes from 17 to 19 at that point the radiators starts cooling down, which it shouldn’t as it’s nowhere near the 30° (which I know it won’t ever reach). I don’t think the TRV is switching the rads off as the rooms/hallways are not overly hot.

    However, on rads cooling down if I mess around with the thermostat I.e in this example I change it from 30 to 28 the radiators will start getting hot again.

    The boiler stays firing throughout from initial thermostat change until i switch it off.

    I don’t understand what on earth is going on, whether it’s my boiler or thermostat?!?!?

    Please help me before I go crazy lol
     
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  3. CBW

    CBW

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    Any ideas how the nest is wired up? Eg opentherm?
     
  4. ianmcd

    ianmcd

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    what is the target CH temp set at on the boiler, and what temp does the display show when the boiler cuts out ?
     
  5. Dangee

    Dangee

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    There aren’t open therm cons on Worcester are there?
     
  6. CBW

    CBW

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    No idea, that’s why I asked.
     
  7. picasso

    picasso

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    Could you narrow it down a bit ?

    Capture.PNG
     
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  8. ianmcd

    ianmcd

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    It is a Worcester Greenstar :rolleyes:
     
  9. picasso

    picasso

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    Combi or system boiler with zone valves ect :rolleyes:
     
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  11. Muj

    Muj

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    Thank you for all the replies guys, I’m an absolute noob when it comes to your questions so apologies for my naivety.

    the boiler is a Worcester Bosch 8000 Greenstar Life Gr8300iw 35 C Ng (that’s what it says on the warranty certificate lol). I’m not too sure what open therm is, the boiler is a standard combi boiler. The trv are danfoss ras-c2.

    I’m not too sure about the target temperature on the boiler, how do I check this?

    All I do is set the Nest thermostat to a target temperature and wait for the house to warm up.

    At first I was thinking it’s faulty TRV but then the towel radiator and my vertical rads which have the chrome valves also cool down so I ruled out the trvs.

    I’ve been speaking to Nest support to see if they can help, but at the moment they’re speaking me through basic troubleshooting which I have already done :/
     
  12. Muj

    Muj

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    I’ve read on another thread which states the Nest thermostat will modulate the water temperature.

    https://www.diynot.com/diy/threads/nest-thermostat-with-open-therm-on-worcester-bosch.554690/

    guy called Jackthom mentions this.

    Is this what is happening to my system? The radiators gets hot for a short while then starts cooling down, is the nest causing the radiators to cool down and why? Because cooling the radiators down will not get me to my target temperature of day 25°
     
  13. snb

    snb

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    I would be checking that the rads are balanced first. Many installers will leave the system with rad lockshields all fully open. Should be balanced.As a quick set up ground floor open 1.5 turns, 1st and second floors only open 1.0 turns.

    Also check that the auto bypass valve ( if it has one fitted is set at about 3.0).

    The nest can only tell a worcester boiler to be on or off ( worcester don't use opentherm)
     
  14. Muj

    Muj

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    The radiators are definitely not balanced. Can an unbalanced system cause this issue?

    not sure what an auto bypass valve is sorry :(
     
  15. snb

    snb

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    Yes because when the nest calls for heat the boiler maybe only pumping around a couple of rads on the top floor. once the boiler flow temp is reached it goes into a waiting period for a few mins before it starts all over again.

    Balance the rads, don't worry about the auto bypass ( if system not balanced then probably didn't have an auto bypass fitted)
     
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  16. Muj

    Muj

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    That’s literally what’s happening!

    The top floor radiators get hot first then the bottom floor.

    I can then hear the boiler after every so often shutting down then making an almost whirring sound then re-firing but the radiators do not get any hotter. Once they’ve reached a hot temperature they cool down then stay constant at that luke warm temperature until i switch the thermostat off and on.

    Does anyone have any idea on the cost of balancing a system?
     
  17. ianmcd

    ianmcd

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    yes absolutely nothing, tell the installer to sort it
     
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