Megaflo Eco thermostat issues (not calling for heat)

Discussion in 'Plumbers' Talk' started by Dave Gibbs, Jan 28, 2021.

  1. Dave Gibbs

    Dave Gibbs New Member

    Hi all,

    Hoping someone here can help me.

    I have a brand new megaflo eco unvented indirect cylinder installed, I also have the nest learning thermostat and programmer fitted and wired in s plan (as per image attached below).

    The big question: when the nest thermostat calls for hot water it heats the water perfectly fine after approx 15-20min but if we are to use the water in the cylinder the water can stay cold for several hours after until the hotwater is again switched on via the nest thermostat. It would seem to me (with my simple mind) that the megaflo thermostat is not calling for hot water and only the nest thermostat calling for it as per the schedule setup or if we override the schedule and turn the hot water on?

    So to be clear if the nest thermostat is calling for hot water the water heats up within approx 15-20min.

    But if we say have 1-2 baths and empty the hot water from the cylinder the water does not then re-heat until the nest thermostat calls for hot water again.

    Here is the wiring diagram that has been used and physical wiring all looks to be in order.

    Any help will be greatly appreciated as currently I am at a loss as to why the cylinder's thermostat is not calling for heat on its own.

    Ps, cable from the nest terminal 3 is connected to cylinder thermostat terminal 1, and cylinder thermostat terminal 2 connected to hit water valve brown.

    Hope this all makes sense and thanks in advance.

    upload_2021-1-28_18-51-20.png
     
  2. Mike83

    Mike83 Screwfix Select

    Nest terminal 3 should go to the heating zone valve not the cylinder stat.
    Is that just a typo.
     
  3. Dave Gibbs

    Dave Gibbs New Member

    Sorry yes, nest terminal 6 to megaflo stat terminal 1

    Megaflo stat terminal 2 to hot water valve brown.
     
  4. Mike83

    Mike83 Screwfix Select

    It’s wired correctly.
    The nest will just send 230v down terminal 6 and through that cylinder stat to the zone valve.
    So your saying the hot water gets used but isn’t getting hot again.
    If the nest is still calling for heat you need to check if voltage is passing through that cylinder stat to the zone valve.
     
  5. Dave Gibbs

    Dave Gibbs New Member


    Please correct me if I am wrong but am I correct in saying that if there is hot water when the nest stat calls for heat then the voltage is passing correctly through the megaflo stat?
     
  6. Dave Gibbs

    Dave Gibbs New Member

    So let's say the nest is no longer calling for heat the cylinder should call for heat when the hot water from it is used and it tops back up.
     
  7. Mike83

    Mike83 Screwfix Select

    If nest isn’t calling for heat then the cylinder won’t heat
     
  8. Mike83

    Mike83 Screwfix Select

    The cylinder stat is just a switch.
    It won’t work unless it’s gets power from the nest.
     
  9. Dave Gibbs

    Dave Gibbs New Member

    Ah this must be my issue, I thought the cylinder stat would call for heat when required regardless of the nest calling for heat?

    So my nest is programmed to call for heat say at 08:00, 12:00, 16:00, 18:00

    If we than bath at 13:00 and use the hot water there isn't anymore hot until 16:00 unless we override the programme and call for hot water but then have to wait until heats up etc.

    Any ideas how I can achieve constant hot water without literally having the hot water on all day, so only when needed?
     
  10. Mike83

    Mike83 Screwfix Select

    What size cylinder do you have?
    Usually it only needs to be on in the morning and evening.
    Mine is in from 6.30-8am.
    4.30-8pm.
    Usually turn it off just before the last bath is run at night.
    I never run out and my tank is about 250l
     
  11. Mike83

    Mike83 Screwfix Select

    So pop it on in the morning 30 mins before you need hot water. It may only need to be on 30 mins depending how much you use.
    Turn pop it on 30 mins in the evening before you need it.
    These things keep warm for hours.
    The smaller the tank the less water you will have available outwith ON times.
     
  12. Dave Gibbs

    Dave Gibbs New Member

    Thanks mate, the issue I have is I have a very large bath (2m x 1m) so each bath nearly completely drains the 250l megaflo I have.

    This means that if say I have a bath, the next bath has to wait for the cylinder to fill back up and heat up which can take some time.

    But I have say had a bath at 8:00 and at 10:00 there is still no hot water until we turn the hot water on from the nest but then have to wait for the water to heat etc. ‍♂️
     
  13. Dave Gibbs

    Dave Gibbs New Member

    Really want to have hot water all day as my house is very sparatic in the way that people all bath at different times, not structure to programme the stat around.
     
  14. Mike83

    Mike83 Screwfix Select

    Turn it on 30 mins before you need it in the morning and off 30 minutes before the last bath at night.
    So that could be 6-30am-9pm.
    Remember your water isn’t on this whole time. The boiler will only come on when the cylinder stat requests it.
    So during this 14.5 hours it may only be on 2.5 hours.
     
  15. Mike83

    Mike83 Screwfix Select

    Or just leave it on all the time.
     
  16. Dave Gibbs

    Dave Gibbs New Member

    Ah ok that make sense, thanks for the help appreciate it
     

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