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Boiler not reaching thermostat temperature

Discussion in 'Plumbing and Central Heating' started by symbiosis, 11 Jan 2019.

  1. symbiosis

    symbiosis

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    Hi all

    I have a fairly ageing TURBOmax VUW 242 Vailent boiler.

    I Have my room thermostat set to 21 but just recently the boiler is cutting out at no more than 17. The rads are hot but the rooms are not!

    I have noticed that the pressure has creped up from a fairly steady 1.5 bar to just under 3 bar

    Any thoughts please?

    Thanks
     
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  3. KenGMac

    KenGMac

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    symbiosis, good evening.

    OK no answer to your pressure fluctuations.

    Can I suggest that you check the validity of the readings that the room stat is giving you, the Stat is set to "XXX" but is the Stat accurate?

    Ken
     
  4. terryplumb

    terryplumb

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    Probably an expansion vessel problem causing the rise to 3 bar. What does pressure drop to when boiler is off ,and cooled down ?
    Raise the target temp on stat to 25 degrees and see what you get !!
     
  5. fixitflav

    fixitflav

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    I'd try turning the boiler control-stat up, see if that helps. There might be a high-pressure cut-out stopping it at 3 bar. The pressure problem needs sorting anyway, probably the vessel as terryplumb said.
     
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  6. symbiosis

    symbiosis

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    thanks for the replies, pressure goes to 2 bar when off (again much higher than before), was also wondering expansion vessel
     
  7. McCombi

    McCombi

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    Undersized rads for the rooms maybe?
     
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  9. Gasguru

    Gasguru

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    Filling loop valves on the T'max Plus are rubbish...there's every chance they are chewed up and allowing the system pressure to rise to mains pressure.
    The vessel will likely be low on charge or failed...needs looking at.
    Have you got the boiler heating thermostat turned up sufficient?
    If the radiator is kicking out heat at say 75 degrees (average across its surface) and the room is not reaching your target temperature it is too small for the rooms heat loss.
     
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  10. John D v2.0

    John D v2.0

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    If the radiators are boiling and the room is not warm enough then there's unlikely to be an issue with the boiler even if it is cutting in and out, it's just doing that to stop the system water overheating until the heat is lost from the radiators
     
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  11. symbiosis

    symbiosis

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    Thanks for the replies, some more info:
    Boiler is shutting off at about 50 on its temp gauge
    Not had this issue previously and house has always been a toasty 21 even in the coldest of weather (its a bungalow so only 6 rads) so i thik can rule out undersized rads

    Would the pressure remain high (2 bar) when off if the pressure vessel needs priming or does that point to something else?
     
  12. Gasguru

    Gasguru

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    You should set the pressure to around 1 bar with the rads cold and the pressure should ideally not rise to more then 2 bar when red hot.
    Does the heating temp control on the boiler respond?
     
  13. McCombi

    McCombi

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    If it’s shutting off at 50 then turn stat higher on boiler
     
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