1. Visiting from the US? Why not try DIYnot.US instead? Click here to continue to DIYnot.US.
    Dismiss Notice

Vaillant 824 bypass valve

Discussion in 'Plumbing and Central Heating' started by SpecialK, 15 Oct 2021.

  1. SpecialK

    SpecialK

    Joined:
    27 Sep 2010
    Messages:
    731
    Thanks Received:
    99
    Country:
    United Kingdom
    Hi,
    I have installed underfloor heating with 22mm pipe from boiler to the manifold. There are two honeywell 2 way valves on the UFH and radiator returns for control.

    When either UFH or radiators call for heat the boiler starts and then gives up. I think it goes in to anti cycle mode? Flame symbol is not lit and d.67 (remaining burner anti cycle timer) starts to count down from 5 mins. When at 0 the flame symbol lights and the boiler heats again...

    When I watch d41 (return temp) it shoots up. The return to the boiler from rads/UFH is cold.

    Is this likely to be an internal bypass issue?

    Why would this start to happen now? Are the honeywell valves really restricting?

    What would be my next steps? Am I right in thinking I should not remove the front cover?

    Thanks....
     
    Last edited: 15 Oct 2021
  2. Sponsored Links
  3. cross thread

    cross thread

    Joined:
    8 Sep 2005
    Messages:
    1,618
    Thanks Received:
    275
    Location:
    worlds end
    Country:
    United Kingdom
    Has it ever worked?Are any valves closed are the zone valves powering open
     
    • Like Like x 1
  4. SpecialK

    SpecialK

    Joined:
    27 Sep 2010
    Messages:
    731
    Thanks Received:
    99
    Country:
    United Kingdom
    As far as I know it has worked OK previously. Not really paid too much attention to it. The house did always heat up quickly so fairly sure the boiler was not cycling like it is now.

    The zone valves must open as the UFH and rads will get hot... Im guessing there is no way to tell if they are fully opening?

     
  5. CBW

    CBW

    Joined:
    26 Sep 2019
    Messages:
    8,953
    Thanks Received:
    2,390
    Location:
    North
    Country:
    United Kingdom
    Any work carried out at the boiler or system recently?
     
  6. SpecialK

    SpecialK

    Joined:
    27 Sep 2010
    Messages:
    731
    Thanks Received:
    99
    Country:
    United Kingdom
    Only me draining the system and soldering in UFH pipework and valves. Nothing boiler related...

    I wonder if something is lodged in the bypass causing it to stick open?

     
  7. CBW

    CBW

    Joined:
    26 Sep 2019
    Messages:
    8,953
    Thanks Received:
    2,390
    Location:
    North
    Country:
    United Kingdom
    If it were the bypass, then the boiler return would be hot underneath. I’m thinking that there’s a valve closed off somewhere too. I was thinking at the boiler, hence me asking.
     
  8. SpecialK

    SpecialK

    Joined:
    27 Sep 2010
    Messages:
    731
    Thanks Received:
    99
    Country:
    United Kingdom
    The bypass is built in to the boiler - I think it bypasses without using the flow and return under the boiler?

     
  9. jackthom

    jackthom

    Joined:
    14 Feb 2007
    Messages:
    1,365
    Thanks Received:
    242
    Location:
    Northumberland
    Country:
    United Kingdom
    Are there valves or filters in the flow and return pipes directly under the boiler?
     
  10. Sponsored Links
  11. SpecialK

    SpecialK

    Joined:
    27 Sep 2010
    Messages:
    731
    Thanks Received:
    99
    Country:
    United Kingdom
    Thanks all for the replies.

    I have cleaned out all filters etc which has helped.

    Now when the radiators are running the boiler is fine. The temp on d.41 (return temp) is as expected.

    When running the UFH d.41 shoots up! It must be bypassing. Are UFH manifolds very restricting? Could it be faulty? Or do I need a valve on that loop to provide less resistance so it doesn't bypass? Maybe a lever valve next to the manifold that's just cracked open...

    Might put a call in to polypipe Monday to see if they have any suggestions....
     
  12. Exedon

    Exedon

    Joined:
    2 Oct 2021
    Messages:
    103
    Thanks Received:
    28
    Location:
    North Notts/South Yorkshire
    Country:
    United Kingdom
    Can you post some clear pictures of motorised valves and pipework to underfloor/boiler. If I read your first post correctly the zone valves are on the return? That's not normal method!
    I'm a polypipe underfloor contractor so may be able to give you some pointers.
     
  13. SpecialK

    SpecialK

    Joined:
    27 Sep 2010
    Messages:
    731
    Thanks Received:
    99
    Country:
    United Kingdom
    I checked the manuals and only the 3 way valves state not to install it on the return. Apparently it doesn't matter with the two ports? The radiators are working fine. Just appears the UFH manifold is very restricting and causing the boiler to bypass and then cycle.

    How accurate should the blending valve be? Mine seems to jump about a fair bit. The input temp is jumping from 40 to 60 degrees but the output temp from the blending valve doesn't seem consistent?

    I didn't get any real instructions with the manifold so I probably don't have it setup correctly at all!

    I will post some pictures in a bit...

    Can you help with the basic manifold settings?
    I have two loops 63 and 66m. What settings should I use for the flow adjustment and pump speed (I,II, Rad or UFH)

    What flow rate should I be getting on the gauges? They are only marked Min and Max...

    Cheers...

     
  14. SpecialK

    SpecialK

    Joined:
    27 Sep 2010
    Messages:
    731
    Thanks Received:
    99
    Country:
    United Kingdom
  15. SpecialK

    SpecialK

    Joined:
    27 Sep 2010
    Messages:
    731
    Thanks Received:
    99
    Country:
    United Kingdom
    D0BE76F3-B7E1-44C8-A1EF-C4764D48336A.jpeg
     

    Attached Files:

  16. Exedon

    Exedon

    Joined:
    2 Oct 2021
    Messages:
    103
    Thanks Received:
    28
    Location:
    North Notts/South Yorkshire
    Country:
    United Kingdom
    The 2 blue caps remove them and make sure actuator pins are moving freely.
     
  17. SpecialK

    SpecialK

    Joined:
    27 Sep 2010
    Messages:
    731
    Thanks Received:
    99
    Country:
    United Kingdom
    Hi, they are free moving. The caps are lightly screwed on and not pushing the pins down.
    When I turn the pump to II the flow shows near max with the flow restrictor set to 30

     
Loading...

Share This Page