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Ravenheat water too hot.

Discussion in 'Plumbing and Central Heating' started by PJfixit, 14 Aug 2014.

  1. PJfixit

    PJfixit

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    Hi this is my first post so greetings to all.

    I have a Raven-heat csi 85t, :( it is getting old but has provided many years of good service.
    The problem is that there is no control over the hot water temperature.
    Once the hot tap is turned on the temperature of the water increases until it reaches scalding point.
    At the moment it is set to water only. I have changed both thermistors but this has not helped. I put a meter on the hot water potentiometer & the resistance changed as I turned it so I assume that is not the problem.

    By the way I am not a heating engineer.

    Any ideas what to try next? Thanks in anticipation.
     
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  3. pallen5000

    pallen5000

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    Does the gas pressure modulate down?
     
  4. PJfixit

    PJfixit

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    Yes, goes up & down with the hot water potentiometer
     
  5. Dan Robinson

    Dan Robinson

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    [​IMG]

    There's a reason we call them Ravenheap.
     
  6. PJfixit

    PJfixit

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    Thanks Dan but I'm not quite sure how that helps me!
     
  7. onlyfitidealboilers

    onlyfitidealboilers

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    So when you turn it to minimum it's still to hot?

    You may want to measure to temp diff of the cold water and hot water bearing in mind that you should have 35c above the specific flow rate?
     
  8. PJfixit

    PJfixit

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    I do not have a thermometer to check the difference. What I can say is that regardless of how the temperature is set the hot water coming out of the tap seems to get hotter until it reaches scalding temp.
    This seems odd as the burner can be seen to change with the temp. control knob. It must make some difference to the temperature of the DHW but even at its lowest it is too hot.
     
  9. onlyfitidealboilers

    onlyfitidealboilers

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    How fast are you running the tap. Remember the slower you run it the hotter the water will be. If you have replaced the thermistors. How do you know your burner pressure is not to high? I've seen it many times where the voltage drops on the modureg but the burner pressure does not alter. My advise now is contact a gas engineer to inspect test and repair this unit.

    Regards
     
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  11. Agile

    Agile

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    He has already told us the gas pressure modulates. Hopefully as evidenced by the flame varying in size.

    My expectation is that he has a very low flow rate. We need to know the flow rate in litres per minute!

    And that a boiler fault is preventing the boiler turning off the flame when the water is too hot. Thats usually a PCB fault.

    But part of the diagnostic procedure is to measure the gas valve parameters. That will need a gas reg engineer.

    Tony
     
  12. PJfixit

    PJfixit

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    I am haring what you both say & yes I have watched the flame height to assess the gas valve modulation.
    I can soon check the flow rate if that helps. We do have fairly naff water pressure but that has been consistent for years whereas the water temp. Issue is more recent.
    Just to confirm I have had the tap full on but still too hot(low pressure does not help, usually about 1.5 bar)
     
  13. Agile

    Agile

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    The flow rate is about 11 li/min.

    If the gas valve settings are correct then the boiler will only modulate to about 1/3 which means any less than 3.3 li/min will get too hot and the PCB should turn off the gas supply to prevent this but this aspect does not seem to be happening.

    Usually a PCB fault but part of the diagnostic process is to check the gas valve settings. That needs an RGI.

    Tony
     
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  14. PJfixit

    PJfixit

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    I think it is time to check the flow rate, I will do this & let you know the result.
     
  15. PJfixit

    PJfixit

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    Just checked flow from hot tap & we are getting 10l/min.
    I am wondering about the merits of changing the PCB as this will be considerably cheaper than calling an engineer out.
    Any thoughts?
     
  16. onlyfitidealboilers

    onlyfitidealboilers

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    Not sure now tbh. I'd not like to guess this seems very odd, if your flow rate is right and it's modulation is working!

    It's up to you but I'd look for an engineer that charged a call out fee but an no fix no fee policy.
     
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  17. PJfixit

    PJfixit

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    You may well be right but I have found a PCB for a good price.
    I will change it over & let you know the result, hopefully in a few days from now.
    Thanks again.
     
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