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main combi 24 he keeps turning on and off

Discussion in 'Plumbing and Central Heating' started by riffraff61, 19 Nov 2010.

  1. riffraff61

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    HI Team

    I have a main combi 24 he (3 years old) which keeps turning on and off again every 20 seconds or so.

    This seems to be on the hot water side only and the heating remains uneffected.

    I have turned the temp setting down a third and it seems okay. If I turn the temp setting back to max then it starts again.

    The gas supply seems good as there are no "low" rings on my 5 ring gas cooker with the heating on full.

    Hot water is good when run at half tap settings but is colder when run full which you would expect.

    I can see some lime build up on one of the main water connections (2nd from the left)

    Pressure is a steady 1.5 bar when heating is off.

    Can the team give me an insight in to what could be causing the error please?

    Thanks

    Riff-Raff
     
  2. spraggo

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    You have either left a hot water tap running or there is a leak on the hot water supply.
     
  3. riffraff61

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    Hi Sparggo - Thanks for the reply

    I only have kitchen sink and bathroom sink on the ground floor - I have checked for leaks behind units etc but nothing wet.

    I have shower unit (fed from the bath taps) and sink in the bathroom. I have checked under the bath and around the sink but nothing showing wet. I have had a feel on the ground floor ceiling as well but there are no signs of damp plaster anywhere.

    I have checked the out-side hot tap and all seems to be okay.

    All header tanks etc have been removed from the loft so there is no water at all up there.

    Hot water supply to the washing machine seems okay as well

    Thanks spraggo
    Riff-Raff
     
  4. riffraff61

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    I have checked all pipes upstairs and they are cold, taps under the sink and to the washing machine are also cold. The pipe to the outside hot water tap is also cold.

    The only pipes that are hot are the pipes to the boiler. most are hot but as the heating is on I am not sure which are heating and which are water.
     
  5. spraggo

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    In that case I would suspect that you have a fault within the boiler, ie, faulty thermostat etc, I would suggest you get a registered gas installer to check it out.

    Regards spraggo
     
  6. braders

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    It could be the plate heat exchanger is blocked.Normally a sure sign when you turn the hot water tap down a little and the water will stay hot.
    It seems also you may have a maximum burner pressure issue with the gas valve on your boiler.
    You need a qualified gas engineer I'm afraid because the starting point for your problem would be there...
    If you are qualified gas engineer then go onto the combustion chamber section of this site and you will find help there.
    Hope this helps..
     
  7. picasso

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    turn off the cold supply to the boiler,if it still fires up its either a sticking hot water flow switch a faulty pcb or the central heating causing the boiler to fire.
     
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  8. riffraff61

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    Call me thick but which of these is the cold supply?
     
  9. Beerlover

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    second from the right.
     
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  10. riffraff61

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    Cold water supply off and the boiler set to water only. Boiler is still firing.

    Is there a way I can test the hot water flow switch easily?

    Thanks

    P.S. I forgot to mention in any of my posts that the fault light is not lit at all.

    There is a electrical box similar size to a plug socket that has one small red LED and a green LED below it. The red LED is on but the green LED is off. I am sure that the green LED is normally lit though. Both LEDs are in the top right-hand corner.
     
  11. picasso

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    drop down the front of the boiler and see if the pin I have marked in red is pressing on the switch, if you have turned the water off this pin should be fully retracted.

    edit ..its not very clear, look where it says microswitch
     
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  12. riffraff61

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    Brilliant picasso, thanks a lot.

    I can see the image well enough, and thanks for taking the time to show me this. (my eye sight is getting that bad that the image was very nearly in focus :eek: LOL)

    Could there be a lime build up within the pressure switch as we do get some hard water problems in this area?

    Riff-Raff
     
  13. picasso

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    there is a small seal around the pin, as it wears it can leak and the pin can get stuck with lime scale ect, is the pin stuck ? if you turn on a tap the pin should come out and then retract fairly quickly when you turn the tap off.
     
  14. riffraff61

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    I would just like to thank everyone who responded to my question. You advise has led me to find the part that is faulty with out the expensive repairman call outs.

    I have identified the faulty part and have started a new thread to find the part that I now require

    Thanks again

    Riff-Raff
     

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