Whys my boiler temp got to 109 degrees?

Discussion in 'Renewable Energy' started by Chippy, Aug 12, 2017.

  1. Chippy

    Chippy Member

    Location:
    Cumbria
    IMG_3897.jpg

    I have a dragon D20 and 14000 litre accumulator tank. I thought the pressure release valves on either the boiler or the tank should prevent this from happening! The one on the tank was hissing a bit. Shouldn't things start getting damaged at 109 degrees? It seems to be working fine but it's cooled down to 100 since this morning
     
  2. skinnyhoskins

    skinnyhoskins Member

    Location:
    the narth
    you need to turn that off,you have a bomb ,
     
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  3. sjt01

    sjt01 Member

    Location:
    North Norfolk
    Could be boiler flow temperature probe failure (although control box should check for this, the one we supplied to Dragon did), or an air pocket round the temperature probe. Also, if the flue damper is not working, chimney draft could be inducing air when no heat is called for.
     
  4. Chippy

    Chippy Member

    Location:
    Cumbria
    It's turned off because when it gets to 90+ it shuts itself down anyway. Where would the flue damper be or do I even have one? For a while now it's been overheating and shutting itself down and I feel like it's drawing too much air in. It can't be faulty temperature probes because the meters in the houses are also saying high temperatures
     
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  5. sjt01

    sjt01 Member

    Location:
    North Norfolk
    I mean the temperature probe that controls the boiler fan. If that is reading low it will run the fan even if the water temperature is too high.
    A flue damper is a balanced flap between the boiler and chimney. If the boiler is hot enough so the fan turns off, and the chimney is hot, without the damper the chimney will draw air through the boiler heating it up further. The damper basically should ensure that the air is pushed through the boiler by the forced draft fan only, and chimney draft just pulls cold air from the base of the chimney.
     
  6. You need to dump some heat.

    That will damage pipes and pipes.

    Check the stats, most likely fault I would say
     
  7. Still Farming

    Still Farming Member

    Location:
    Glamorgan Wales
    On top of it is a pressure relief value and should blow at 1.5- 2 bar.
    WD40 it When cool -sticks sometimes.
    As said dump heat -rads or what ever FULL all on ?
    Turn fans off .
    Do 'nt open boiler door as more air -more burning .
    What are you burning - could be reason too .
    Temp.stats may be faulty too .
    Take care .
     
    Chippy likes this.
  8. Chippy

    Chippy Member

    Location:
    Cumbria
    I'd just started putting big logs on as opposed to bundles of split logs because I thought big logs would burn slower and I wouldn't need to load as often. I'd also just started loading before previous load had burnt out so I wouldn't need to light it as often and I hoped boiler would hold its temp at the set 75 degrees so I wonder if it's drawing air in because it's overheated a lot but never got above 95 before
     
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  9. Still Farming

    Still Farming Member

    Location:
    Glamorgan Wales
    As you open door will increase temp.
    Logs got more latent heat and holds heat more too .
    What's temp.pressure gauge say ?
     
  10. f0ster

    f0ster Member

    with a log burner it is important to not let it slumber, ( when the buffer is up to temp there has to be no fuel left in the chamber)
     
  11. Fowler VF

    Fowler VF Member

    Not a good place to be for all of the above answers. But then again, you asked the question should the pressure relief valve have blown before it got to this stage? Well at 109 degrees C the water isn't boiling if the pressure is above 1.38 bar. So if you have a 2 bar relief valve then it wont have blown off until the temperature gets up to nearer 120 degrees. This is definitely not a good place to be at all; if you had a pipe burst then dumping all that hot water onto the floor at 1 bar (atmospheric) pressure would mean that none of the water wanted to be water it will instantly turn to what it should be at that pressure and temperature, i.e. steam. Steam occupies an awful lot more space than water, so it has to rapidly expand its volume, so a wall of steam at 100 degrees plus blasts through the building trying to find its way out. I am describing a flash steam explosion!! Its why people get scalded when they undo a radiator cap on an engine; but the engine wasn't boiling they say, through the bandages!

    Upshot of all this is you need to have some more safety measures in there. NEVER rely on just the pressure blow off, you need something that shuts down the production of heat on temperature, way before it starts to affect pressure. One of the big problems with a batch boiler system is how do you stop it completely when the system has reached temperature. The slightest bit of draft into the fire, or opening the door just makes it worse. Must have a heat dump, and preferably one that is gravity fed in case of power failure. Rising pressure also raises the boiling point and therefore hides the problem until she blows!
     
  12. Chippy

    Chippy Member

    Location:
    Cumbria
    I think the reason nothing was damaged etc is because the expansion vessels never reached there limit. Tested all the blow offs and they work fine. There's no way air can get into the boiler on a dragon other than through the fan which was shut down. There shouldn't be any air pockets because I could hear the air bleed valve letting air out. What's easiest way to make a heat dump that's triggered when it hits a certain temp?
     
  13. Still Farming

    Still Farming Member

    Location:
    Glamorgan Wales
    Big radiator and fan off lorry is it ?
    Or another circuit you could open up is it ?
     
  14. Chippy

    Chippy Member

    Location:
    Cumbria
    IMG_3923.jpg

    It doesn't help that even though the set temperature is 70, the fan is still running at 10%. Can't seem to stop it. Might need to get guy that built it to alter software on it
     
  15. Still Farming

    Still Farming Member

    Location:
    Glamorgan Wales
    Bit too high tech. that for me .
    Get old fashion gauges and stats. fitted - cheaper and more straight forward .
    What's Dragon say ?
     
  16. Chippy

    Chippy Member

    Location:
    Cumbria
    Dragon just say what you guys have suggested really. I'm regretting testing the blow off on the tank because now it won't stop running water. Can they be taken to bits?
     
  17. f0ster

    f0ster Member

    It is often a problem with a blow off. They can get dirt under the seat. With your boiler it is better to only load it enough to get the buffer to the temp required. Other wise is will be slumbering. (Fuel in the chamber but no heat needed)
     
    Fowler VF likes this.
  18. Still Farming

    Still Farming Member

    Location:
    Glamorgan Wales
    Wd40 it well
     
  19. Fowler VF

    Fowler VF Member

    Agree entirely. My guess is that the control system we saw the photo of is keeping that 10% blower rate up so that if there is any wood left in the chamber it isn't being starved of oxygen and is able to quietly smoulder. Starve it of oxygen and it will have a tendency to gasify; chamber would build up with wood gas and next time you opened the door or switched the blower on the gas would go up rather quickly. Not so much of a problem with a smaller boiler but a bit of whoosh on a big one with a big door!
    If you have put more into the thing than is needed to heat up the buffer tank and immediate needs then even that 10% blower rate will quietly go on producing more heat and give you the issues you had. I have seen systems where as well as the over pressure relief there is also a water dump valve run by a thermostat, can only really do this if there is an auto top up system filling it back and in any case the issue is then one of a lack of correct inhibitor treatment in the fresh water. That sort of mechanism isn't meant to be one in regular use, its just another safety feature to back up the pressure relief.
     
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  20. Still Farming

    Still Farming Member

    Location:
    Glamorgan Wales
    The heat meters etc. Don't like inhibitor so if you got in there may effect gauges ?
     

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