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boiler temp question

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  • boiler temp question

    I recently adjusted my boiler temp on my Isomac Tea and now my pump pressure is not running at 9 bar. Does adjusting the the boiler temp affect the pump pressure?
    Last edited by FineGrind; 17 November 2012, 06:49 PM.

  • #2
    Not to my knowledge. Temp adjustments should have no impact on pump pressure.
    I thought the Isomac Tea was a HX machine, so how did you adjust the boiler temp?


    • #3
      There is a brass screw that you can reach by taking of the warming tray and putting a screwdriver through the grill. It adjusts the boiler pressure. But I didn't think that was the pump pressure. Is it?


      • #4
        Hi FG

        You stated "I recently adjusted my boiler temp on my Isomac Tea and now my pump pressure is not running at 9 bar."

        And then

        "It adjusts the boiler pressure."

        Which one did you do

        I would think you adjusted boiler pressure by adjusting the over pressure (safety) valve.
        It basically sets the MAXIMUM brew pressure and stops the boilers from exploding from too much pressure in a worst case.
        So in effect, the pump pressure never changes unless the pump is worn or broken, with the excess pressure being fed back into your water tank (there should be 2 tubes into the tank, one for pick up & one for return)
        I assume you have a gauge on the machine telling you the pressure. This is pressure at the boiler, not the pump.
        And finally none of this has anything to do with temperature.

        Hope this makes sense and helps.


        • #5
          boiler temp question

          Sounds to me like you simply adjusted the pressurestat? This shouldn't effect the brew pressure though, only the boiler temp.


          • #6
            On the Tea, the pressure stat can be adjusted with the use of a screw driver through one of the holes under the cup tray. (NB this should always be done with the machine UNPLUGGED - not just off. 240v kills - quickly and painfully). This changes the at what pressure the element switches off for boiler pressure only.

            The bypass valve/OPV for pump pressure is located underneath the boiler. To get to it, you have take off the cup warming tray, take out the tank, slide out the metal cover that covers the boiler and that the water tank rests on. The following picture shows side view if you take the side panel of the machine off.

            So yes FineGrind, I'm 100% sure you adjusted the pressure stat.

            Try putting a blind filter in and seeing what the pump pressure gets to then. If it reaches over 9bar (just like it did before), then its grind/dose/tamp. If it doesn't reach 9bar (or where it got to before the adjustment), and you're 100% sure the only change you made was to the pressure stat, then some spooky magic is going on that someone more knowledgable in the dark arts will have to advise you on.

            If FineGrind changed the boiler pressure down so far that the water coming through the group is too cold - could that make the brew line not reach full pressure? My guess is maybe - but you'll be seeing gushing blond shots tasting like lemon which would be a much bigger indication than a number on a gauge.


            • #7

              off the cuff without having a machine in front of me:

              I assume you adjusted the boiler / steam pressure because the machine most likely has a vibrating water pump in which case i doubt there is a "brass screw" on the bypass valve coming from the water pump (more likely a brass union to turn with a spanner, not a screwdriver)....and in any case most manufacturers would view an adjustment to the water pressure as being "non user serviceable" and would not likely allow an end user easy access to fiddle with it.

              In which case I would have to say that yes, it seems you've likely adjusted the boiler / steam pressure and no, what you've adjusted wont affect the water / group / brew pressure which is unrelated to the boiler / steam pressure.

              So if there is now a problem with brew pressure, I imagine the reason will lie "elsewhere" with the quickest / easiest thing to pick on in such situations (semi commercial machine with vibe pump and water pressure gauge) being with the coffee grind, the coffee freshness, or a change in your technique.

              Essentially, the more back pressure you provide at the group (things like finer grind OR harder tamp OR larger dose OR fresher beans without corresponding grind adjustment) will usually indicate a greater pressure at the water pressure gauge and a slower flow from the group handle outlets / and of course, vice versa for lower indicated pump pressure.

              OR.......if for some reason your machine is now not reaching a proper operating temperature and is only flowing luke warm water, the rate of coffee oil extraction will be far less than it should be, resulting in less back pressure at the group, and the indicated water pressure on the gauge will be lower than it should. But that would require you to have made a HUGE boiler pressure adjustment (to have decreased the water temperature that much)....and you would have a very low steam pressure (indicated on the gauge), not rising to where it would normally go.

              You havent actually told us what has changed about your water pump pressure (during brewing), and when all else fails you could also try readjusting what you adjusted, back to where it was before......

              Given you a few variables will need to pick one, or take the machine in for service.

              very first CS site sponsor

              PS there can be some confusion in the terminology and I hope the following helps:
              A "safety" or boiler "over pressure" valve is a valve that just sits at the top of the boiler & sets the steam / boiler safety relief pressure in the event that the element is not switched off and the boiler pressure keeps climbing. It is entirely SAFETY related AND MUST NOT BE FIDDLED WITH (or you could turn the boiler of your machine into a bomb waiting to go off).

              It has nothing to do with coffee making but it does sometimes get confused with the water pump "bypass valve", because some people call that (the pump bypass valve) an OPV (over pressure valve)...and if we are going to call that an OPV, it needs to be noted that it is not the same OPV as that which is at the top of the boiler......which is the safety relief valve mentioned previously ie....there can be two OPV's depending on anyone's use of terminology...and they are not related to eachother.

              And then of course, a boiler OPV IS a safety valve, but a water pump OPV is NOT a safety valve.

              And all of that is why I prefer NOT to call the pump bypass valve an OPV (but of course we can all do whatever we like)!

              I hope that is not confusing.

              And I hope that helps.
              Last edited by Fresh_Coffee; 18 November 2012, 04:05 PM.