Smart fit Megaflo : 2 port valve query..

Discussion in 'Plumbers' Talk' started by Guido_22, Nov 30, 2019.

  1. Guido_22

    Guido_22 New Member

    Hi
    I am trying to suss out why the 2 port valve on my heating system is on the pipe (labelled 'return') from the outlet of the hot water cylinder.

    When I set the programer to call for heating only.. this 2 port Honeywell valve on this pipe from the cylinder, opens.

    I know the airspace on the Megaflo needs a periodic top-up which I have done and do every 5 months or so... but I get a drip via the tundish to outside and about 12 months back replaced both the combination valve and the TPRV figuring they were causing the problem. I still have the drip to outside.

    I can't understand why the 2 port valve would open when the system is calling for heating only. Surely this should stay closed - but the 3 port actuated valve on the flow from the pump, should set itself to divert flow around the heating circuit only thus bypassing the cylinder.

    As it is, I suspect the HW in the cylinder is overheating and causing the drip.
    Any ideas what I can do to fault find further would be much appreciated.

    Thank you.
     

    Attached Files:

  2. Guido_22

    Guido_22 New Member

    It is a system fit valve ie. as supplied by the manufacturer, so must be right.
    Just don't understand why it operates as it does...
     
  3. Mike83

    Mike83 Screwfix Select

    The valve would need fitted if it came with the cylinder.
    But it’s probably just wired wrong so it opens whenever the boiler gets a demand.
    Does it wire straight into the pcb on either the pump or boiler terminal. The smartfit doesn’t really have anywhere else to connect it.
     
  4. Mike83

    Mike83 Screwfix Select

    Another thing.
    I’m not sure how your cylinder sensor can work in series with the cylinders overheat cut out.
     
  5. Guido_22

    Guido_22 New Member

    It's wired into the terminal on the cylinder ..
     

    Attached Files:

  6. Guido_22

    Guido_22 New Member

    If I post a picture of the wiring in the terminal on the cylinder, would that help?
     
  7. Mike83

    Mike83 Screwfix Select

    Yes
     
  8. Guido_22

    Guido_22 New Member

    There you go..
     

    Attached Files:

  9. Mike83

    Mike83 Screwfix Select

    The additional zone valve has been wired through the hot water overheat.
    This is wrong but would almost do the same job.
    The Honeywell smartfit isn’t really compatible with an unvented cylinder.

    the cylinder sensor does an important job.
    I can’t see where it terminates. It should ideally go into an insertion tube if it’s the ntc type.
     
  10. Mike83

    Mike83 Screwfix Select

    Where do these cables all go.
     
  11. Guido_22

    Guido_22 New Member

    You should be able to tie up with the picture I posted earlier of the whole system?...
    But the narrow black cable goes to the pump, the thicker black cable goes to the 2 port valve.. The white cable goes to the Smartfit controller..
     
  12. Mike83

    Mike83 Screwfix Select

    So the pump and 2 port are fed through the overheat stat.
     
  13. Mike83

    Mike83 Screwfix Select

    38892933-6716-4EA1-9C98-9273E580288D.jpeg Where does this go
     
  14. Guido_22

    Guido_22 New Member

    The cylinder sensor wire goes from the controller into the cylinder wiring terminal .. it is hidden behind the thick black cable on the wiring photo on the right hand side and appears to go behind the plate that is shown... I presume to the cylinder thermostat ...
     
    Last edited: Nov 30, 2019
  15. Mike83

    Mike83 Screwfix Select

    The sensor wire needs to be inserted into an insertion tube to work correctly. If not it won’t detect the cylinder temperature accurately.
    It’s also wired that if the cylinder overheats it will close the 2 port valve and turn off the pump. Not the best tbh.
    When the cylinder overheats it should only stop the HW from working.

    Smartfit can’t be wired through the cylinders built in thermostat.
     
  16. Mike83

    Mike83 Screwfix Select

    Personally I would get rid of the smartfit (obsolete) and change to a s plan system.

    This would then ensure the system can be wired correctly and in a safe manner.
     
  17. Guido_22

    Guido_22 New Member

    As you may have guessed I am no Plumber, but having read around the Web,i was led to believe given it has a three port valve to divert to either hw or Ch, or both(?) this was an S plan system...?
     
  18. Guido_22

    Guido_22 New Member

    I believe myself to be reasonably technically competent.. What would be involved if the Smartfit control is removed... What control replaces it and presumably the zone valves would all be fitted just after the pump..?
     
  19. Mike83

    Mike83 Screwfix Select

    Y plan.
    But because you have an unvented cylinder the HW required a 2 port zone valve.
     
  20. Mike83

    Mike83 Screwfix Select

    2 zone valves fitted after the pump. Yes.

    All the smartfit would need removed. It’s not compatible with anything else.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice