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Radiators are very hot, even with boiler temp turned right down

Discussion in 'Plumbing and Central Heating' started by longrob, 11 Nov 2018.

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  1. longrob

    longrob

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    I have a Worcester Bosch boiler Greenstar 37CDi that is about 8 years old.

    I have noticed that our radiators get very hot. So I have turned down the temperature to it's lowest level - but the radiators remain very hot. In fact it appears that the temperature control is having absolutely no effect whatsoever. The attached picture shows the situation. The boiler was serviced about 6 months ago and I have been observing this problem for about 4 weeks. I have tried resetting it, as well as turning it off completely.

    I don't know if it is relevant, but even with the hot water temperature turned right up, our hot water is only *just* hot enough for a bath or shower. It has been this way since the boiler was installed.

    I would appreciate any help or advice, as I can't really afford to call out a heating engineer at the moment.
     

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  2. picasso

    picasso

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    At a guess your diverter valve is stuck, I see from the pic the eco function is on (dhw preheat turned off) is it normally like this or do you have the preheat turned on ?
     
  3. longrob

    longrob

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    Thank you. I normally have pre-heat switched off (eco on) but occasionally leave it on by accident after a reset.
     
  4. longrob

    longrob

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    Any suggestions for what I can do to solve this ?
     
  5. terryplumb

    terryplumb

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    When you had the boiler serviced 6 months ago , and you had an issue then with low domestic hot water temperature ,what did the engineer diagnose or recommend to resolve this ? With regard to the radiators temperature , do you have a wall thermostat ?
     
  6. longrob

    longrob

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    Unfortunately I didn't mention the hot water temperature, since it is adequate for our needs (I just mentioned it above in case it was relevant to the radiator temperature)

    Yes, we have a wall thermostat / digistat, which seems to fire the boiler up when needed. It's just that after the boiler has fired up for a while, the radiator temperature seems excessive (to the point of almost scalding) and the boiler control doesn't seem to reduce it.
     
  7. terryplumb

    terryplumb

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    When your rad temperatures get to the " almost scalding" point what temperature does the boiler display show ? When your wall stat is not calling for heat ( set temperature reached / satisfied ) does boilers burner shut down ,or remain alight ?
     
  8. longrob

    longrob

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    The boiler seems to stay around 55-65 degrees C when the radiators are hot.

    I am not sure what it does when not calling for heat - I will investigate when I get home this evening - thanks !
     
  9. terryplumb

    terryplumb

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    You posted earlier that the boilers c/heating temperature selection dial had no effect whatsoever , if you turn it up to its highest setting ,does the temp at boiler increase or not ?
     
  10. longrob

    longrob

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    I have investigated. After the room temperature reaches the desired level, the boiler stops and the temperature display falls to around 36 degrees.
     
  11. longrob

    longrob

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    Yes, it goes up even higher - it reached 79 before I got a bit scared and turned it down. But it wouldn't go lower than 55 until the desired room temperature was reached.
     
  12. terryplumb

    terryplumb

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    Then you will need an engineer to visit. You have more than one issue ,the domestic hot water isnt getting hot enough and c/h temp too high on lowest setting. Not likely something that you can sort yourself.
     
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