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

Vaillant boiler, no hot water but heating ok!

Discussion in 'Plumbing and Central Heating' started by Highflyer380, 11 Oct 2019.

  1. Highflyer380

    Highflyer380

    Joined:
    11 Oct 2019
    Messages:
    4
    Thanks Received:
    0
    Country:
    United Kingdom
    Hi,

    I have a Vaillant EcoTec Plus 630 boiler with a Heatrae Sadia CL250S28 Megaflo.

    The boiler is working for the underfloor heating and the central heating, but is not heating the hot water.

    The motorised valve for the hot water on the megaflo is open, and the overheat reset on the tank is ok, but there doesn’t appear to be a demand for the boiler to fire up coming from the hot water system!

    Adjusting the thermostat on the megaflo opens and closes the motorised valve.

    The pressure in the system is fine and the programmer is set correctly and working ok.

    Any ideas please?
     
    Last edited: 11 Oct 2019
  2. Sponsored Links
  3. stem

    stem

    Joined:
    20 Jul 2005
    Messages:
    5,896
    Thanks Received:
    1,251
    Location:
    Nottinghamshire
    Country:
    United Kingdom
    The motorised valve has a small microswitch inside it that is responsible for operating the boiler when the valve is open.

    However, in your case I would still expect the hot water to heat up if the valve is open, because the boiler will be operating because of a demand from the heating. Being part of an unvented system, you would probably be best advised to get a professional (Someone with a G3 certificate) in for fault finding.
     
  4. Highflyer380

    Highflyer380

    Joined:
    11 Oct 2019
    Messages:
    4
    Thanks Received:
    0
    Country:
    United Kingdom
    So, replacing the Honeywell twin port motorised valve head is the most likely cure?
    The hot water is flowing through the valve when the heating demand is there.
     
    Last edited: 11 Oct 2019
  5. stem

    stem

    Joined:
    20 Jul 2005
    Messages:
    5,896
    Thanks Received:
    1,251
    Location:
    Nottinghamshire
    Country:
    United Kingdom
    In that case, a faulty switch inside the head would cause the symptoms you describe.
     
  6. Highflyer380

    Highflyer380

    Joined:
    11 Oct 2019
    Messages:
    4
    Thanks Received:
    0
    Country:
    United Kingdom
    I have replaced the motorised valve head......still doesn’t work!
     
  7. Highflyer380

    Highflyer380

    Joined:
    11 Oct 2019
    Messages:
    4
    Thanks Received:
    0
    Country:
    United Kingdom
    So I fiddled around and swapped the programmer for a spare one and then back to the original, still didn’t work. Then I reset the air gap on the megaflo and it now works!!
    Don’t understand it it, but as long as it works now!!
     
  8. stem

    stem

    Joined:
    20 Jul 2005
    Messages:
    5,896
    Thanks Received:
    1,251
    Location:
    Nottinghamshire
    Country:
    United Kingdom
    Rather strange indeed :confused:

    If the "air gap" was the problem, how would the water heat up OK when the motorised valve was open and the central heating was switching the boiler on.

    The valve opening, and the boiler not firing up all points to a control issue. It wouldn't be the programmer, if that was faulty, the motorised valve wouldn't open.

    Maybe there's a loose wire somewhere and you disturbed it at some point and so it's working again.

    As you say, at least it's working for now.
     
  9. Sponsored Links
Loading...

Share This Page