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Thread: Silvia issue running too hot?

  1. #1
    Junior Member
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    Aug 2005
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    Silvia issue running too hot?

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hi everyone,
    I think my Silvia has begun to run too hot, and all my shots seem way hotter than they used to.

    To test this I placed a thermocouple probe under the screw that holds down the brew thermostat (closest to the inlet).
    What i discovered was that it thermostat comes on at about 85oC and turns off at 107-108oC.
    Now from memory I think this is normal however the over shoot raises the boiler to between 120-126oC
    Also the boiler heats (with no water flow) in 38 seconds which seems very fast and would thus help explain the over shoot.

    So my question is the thermostat failing or is the boiler element on the verge of exploding?

    Any feedback would be helpful
    thanks


  2. #2
    Senior Member
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    Jan 2007
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    541

    Re: Silvia issue running too hot?

    Howdy agent86,

    welcome to coffeesnobs.

    All of what you mentioned [temp and cycle wise] sounds about right.

    Check out this link from sitesponsor "pidkits", as it plots pretty much what you found [ie max temp 239F=115C, min temp 196=91C]:

    http://pidkits.com/temperature.html

    A thermostat can be thought of as a bimetalic strip [two straps of different metals with different thermal characteristics taped together]
    As it heats each strip will expand at a different rate and eventually will bend causing an electrical contact to open.
    Typically in a Silvia this occurs at 110C which is what you are seeing.
    The strip requires some cooling before it will return to its original position, hence the 85C. This range is known as a thermal deadband.

    Added to the deadband of the thermostat, is the deadband of the system. The heating element of the boiler is quite large with respect to the internal of the boiler and even when the thermostat switches off the power, the thermal energy [heat] stored in the element, will continue to heat the water in the boiler.
    Think of an electric stove top, you switch it off and it will still keep heating for a while.
    The thermal mass of the brass boiler and the water itself all contribute too.

    Optimum temp for a brew is in the range 94 - 96C measured at the puck. Your measurements are taken at the boiler which is approximately 10C higher.

    The object is to pull your shot when the brew water is at the right temp.
    With your thermometer, you could watch for a boiler temp of say 107C and then pull the shot.
    If you dont intend to Keep the thermometer connected, watch the cycle of the machine [take it from a reference such as boiler light goes on]

    Google "temp surfing silvia" and youll open a big can of worms

    Good luck with it.




  3. #3
    Junior Member
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    Aug 2005
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    Re: Silvia issue running too hot?

    Thanks Reubster for the detailed feedback and tips, i think i was doing it all wrong, Ill try some those things at least until i can afford to add a PID to the machine

  4. #4
    Senior Member
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    Jun 2006
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    Re: Silvia issue running too hot?

    Im not sure if this is what youre talking about, but the body of my Silvia feels a lot hotter at this time of year, and yes, shots seem hotter as well. Its just a flow on effect from the weather warming up, youll get used to your machine being that warm, and in about 6 months time youll suddenly notice that she seems to be running a little cooler.

  5. #5
    Mal Dimal's Avatar
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    Re: Silvia issue running too hot?

    Quote Originally Posted by Viviane link=1225932633/0#3 date=1225961045
    Im not sure if this is what youre talking about, but the body of my Silvia feels a lot hotter at this time of year, and yes, shots seem hotter as well. Its just a flow on effect from the weather warming up, youll get used to your machine being that warm, and in about 6 months time youll suddenly notice that she seems to be running a little cooler.
    I think youve hit the nail on the head Viviane [smiley=thumbsup.gif]... I noticed similar goings-on with my Imat Mokita before fitting a PID Controller to manage the Boiler. The effect was still noticeable but greatly diminished....

    Mal.

  6. #6
    Junior Member
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    Aug 2005
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    Re: Silvia issue running too hot?

    Thanks for the feedback everyone,
    now i understand the problem better: the boiler under the control of the brew thermostat should top out at about 115oC but mine was getting up to 125oC which meant that when i let the machine warm up it all the metal mass that helps regulate the water temperate when brewing was way too hot therefore there was no way i could make any brews that also not too hot.
    After thinking about the feedback here and the fact that the machine 4 years old now, I thought that maybe the problem was simply that the thermostat was not getting good contact with the boiler, and on investigation i could see that the old heat transfer compound had dried out.

    So after applying some new heat sink compound on the thermostat the problem seems fixed: it now turns off earlier and "only" rises to between 115-118oC.

    I guess the next step is to start saving for a PID and hope the value AU$ improves



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