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Boiler heats water quick then shuts down

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BP007
BP007 Member Posts: 3
in THE MAIN WALL
My CH boiler (combi sealed system Baxi 105e instant) the pump works the timer works but when Boiler fires up to heat water for rads the heating cycle lasts about 1 min before the boiler registers water has reached max temp and then stops firing. About five mins later it all happens again and does this constantly whilst boiler is programmed to heat rads. Hot water (hot water to taps)system works fine, however sometime the hot water only heats to about 40-50 degrees. All rads are warm but never get hot due to this. Anybody know what the problem might be. Oh!! it used to work fine. I've drained the system and flushed it. No change.

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  • Tom_133
    Tom_133 Member Posts: 884
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    My guess is the near piping at boiler is not correct or not sized properly, or if this is a new problem maybe you have a bad pump. How about some pics?
    Tom
    Montpelier Vt
  • BP007
    BP007 Member Posts: 3
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    Thanks for response Tom.
    It is a problem that has started this 'season' Ive not altered any pipework. I thought it may be the pump so I changed the pump, the problem still occurs.
    For further explanation..... when the boiler fires up the water leaving the boiler gets very hot and the 'pipe'(feed) quickly gets too hot to touch, the boiler then stops firing, the pipe cools, the boiler then fires up again, its almost like there is a blockage , but all the radiators do get warm so how can there be a blockage? What photos would you like?
  • quack24
    quack24 Member Posts: 74
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    could be a zone valve try opening them manualy
  • quack24
    quack24 Member Posts: 74
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    or the circulator relay test to see if you are getting 120 by the circulator while ther is a call for heat happens all the time that a circulator doesnt work and the radiators still get hot because hot water is less dense than cold water and will naturally "float" up to the radiators
  • quack24
    quack24 Member Posts: 74
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    post some photos of the near boilers piping
  • Zman
    Zman Member Posts: 7,569
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    This reads like a flow issue. Is it air locked?
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • Tom_133
    Tom_133 Member Posts: 884
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    If the boiler is getting hot enough to shut down, and the radiators are getting "warm" as Zman said it seems like a flow issue. Do you have radiators, or baseboard heat? Also, any pics of the boiler piping would be good, just not too close we want to be able to see how everything is piped.
    Tom
    Montpelier Vt
  • BP007
    BP007 Member Posts: 3
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    Thanks for all the comments it is really appreciated.
    The system is relatively old, the installation has been in for approx. 15yrs. All rads.... some first floor some ground floor, even split. Boiler has been regularly maintained and from time to time new parts have been fitted when required. New pump fitted earlier this winter.
    Unfortunately majority of pipework is concealed the only photos I can get is the immediate pipework close to boiler. I will post some a little later.

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