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Isomac Millenium - HX Heating Cycle Issues

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  • tomo88
    replied
    Too easy, thanks for the feedback. Upon going down the rabbit hole last night, makes sense and seems like those numbers are legit, albeit pressure maybe a bit high but I can play around with the pstat. I'll open her up to confirm its just the vac spitting and nothing out of the ordinary. I guess when a PID cycles, it's cycling at rates of potentially 100 times a minute and are very small flashes of energy draw as opposed to the HX and cause it's all done behind electronics as opposed to mechanical, you don't really see/hear it. Cheers for the help, good learning

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  • Javaphile
    replied
    A system using a PID controller does not retain heat for longer than a machine using a pressurestat! Neither one has any effect on how much heat is retained by the system. Heat retention is determined mainly by whether or not the boiler is insulated or not insulated. PID controllers can maintain a more consistent boiler temperature/pressure than a system using a pressurestat as they have a narrower dead band which means they're actually cycling more frequently than a machine using a pressurestat.


    Java "The method of temperature control has nothing to do with heat retention!" phile

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  • tomo88
    replied
    Appreciate the feedback noidle22 . Ive potentially been spoilt by PID then, honestly would have thought it would be able to retain heat for longer than 90 seconds... I used to have a Saeco via Venezia and even that didn't cycle as much as this did. I thought with a larger boiler and then design of the e61, it had a large thermal mass. I'll pop open the cover and watch it while running but good to hear other HX experiences. I can certainly see why PID is the way to go these days.

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  • noidle22
    replied
    Sounds pretty normal, unless you can hear a steam leak from the machine then it's working as expected. A heating cycle every 90 seconds is pretty good, better than a lot of machines out there.

    1.5 bar is quite high for a standard HX machine though unless it's had the thermosyphon loop modified (however you can't always trust gauges on second hand machines).
    No way of knowing if this is the case unless you check the upper thermosyphon tube at the group head. Most unmodified HX machines like this run around 1.2-1.3 bar max pressure. A normally functioning pressurestat will have a 0.2 bar deadband (eg switches off at 1.2 bar, back on at 1 bar).

    If you find it to be overheating and steaming/sputtering from the group head excessively when you lift the lever, reduce the pressure to the 1.2-1.3 bar range then try again after the machine has stabilised (run a cup of water through the group then let the machine idle for 20-30 minutes). Some steaming/sputtering can be expected if the HX loop hasn't been modified, this is normal.

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  • tomo88
    replied
    Thank you for the feedback. I will check the vac as it seems like easier access from the top as opposed to requiring to take off the whole cover. Thanks for the explanation on the pressurestat and deadbands. Did a quick google on that too and makes sense. I understand that coming from a PID machine to this that stability will not be as good but to power cycle every 2 minutes seems excessive to me; if this is normal happy to accept that but seems like it would suck a lot of power over idle.

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  • Eastlink Espresso
    replied
    On HX machines pressure is either regulated by a pressurestat or in modern days by PIDs.
    Adjusting a pressurestat will effectively set the contacts so that a lower or higher pressure will close the contacts. This normally accomplished by a screw located on top of the pressurestat. Essentially you are preloading a spring which would then compress with the steam coming from the boiler.
    All pressurestats have a deadband. That is the number of degrees between when the pressurestat turns on and when it turns off. If too large there you will end up having low pressure and the brew temperature will surf quite often. If too narrow the pressurestat won't last long.
    Manufacturers had to deal with this for many years and recently have equipped HX machines with PIDs, though they are not exactly vital, they are more refined for and can improve thermal stability.



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  • topshot
    replied
    You could start by checking the anti vac valve is not leaking at all.

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  • tomo88
    started a topic Isomac Millenium - HX Heating Cycle Issues

    Isomac Millenium - HX Heating Cycle Issues

    Hi All

    Recently purchased an Isomac Millenium second hand as I wanted to give E61 a go (replacing BES920).

    I received today and noticed over 10-15 minutes that the pressure gauge would heat to 1.5 bar, then drop to 1.2 bar over approx. 90 seconds which would kick in the pressure stat. This would trigger the heating element and then it would heat back up to 1.5 bar over 10 seconds and repeat. The rest of the machine is quite hot, including the group head so shouldn't be losing heat to that. This is all with all valves closed and sitting idle.

    My experience with HX's is non-existent having only used a single boiler thermostat and dual boiler PID. Even the single boiler with thermostat seemed to hold heat at idle however, just wanted to see if this was normal amongst HX machines. I would have thought it would hold stable for a lot longer.

    Cheers, Tom
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