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Thread: Domobar Super thermosyphon / cooling flush issues

  1. #1
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    Domobar Super thermosyphon / cooling flush issues

    Gene Cafe Coffee Roaster $850 - Free Beans Free Freight
    Hello

    Ive owned my early model Domobar Super HX for a couple of months now. It was in need if a good once-over when I got it, so I descaled the boiler and all associated pipes and HX, and removed, disassembled and cleaned the grouphead.
    Overall it works great now, however occasionally (perhaps once every fifth or sixth start up), the group head will be only warm to the touch after a good 45min warm up. Other times the grouphead will be hot but when I do the initial cooling flush following warm up there is no flow at all out the grouphead for around fifteen or so seconds.

    Is this behaviour considered to be a “normal: non-normal” characteristic of these machines or is there something that I should address? A possible intermittent blockage in the thermosyphon circuit? An issue allowing the water in the grouphead to drain back and not be refilled until the pump is turned on? Other?

    Many thanks
    Neil.

  2. #2
    Mal Dimal's Avatar
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    Quote Originally Posted by Cresco750 View Post
    A possible intermittent blockage in the thermosyphon circuit? An issue allowing the water in the grouphead to drain back and not be refilled until the pump is turned on?
    G'day Neil...

    This is something I would definitely check.
    What type of descaler did you use, out of interest?

    Mal.

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    Thanks Mal. I used a commercial citric acid based descaler, followed by a mild food grade citric acid brew. There was quite a bit of scale flake inside the boiler so I ended up turning the machine upside down and flushing it with the hose. I also back flushed all the pipes. It is possible that a stray piece of scale lodged itself somewhere, I guess?

    How do you suggest I check the thermosyphon circuit? I read that some of these machines have a restrictor in the circuit somewhere?

    cheers

  4. #4
    Mal Dimal's Avatar
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    Hello again mate...

    Yeah, that's the trouble with Citric Acid based descalers in that they tend to loosen a lot of scale flakes that are then likely to be drawn into all the small orifices in the brew circuit and elsewhere. Commercial descaling compounds such as "Clean Machine Triple Action Descaler" do a much better job as they dissolve scale particles such that they can then be flushed away without being trapped somewhere in the system.

    Descaler.JPG

    You may have to go back and disconnect all pipework, etc and then individually flush everything out very thoroughly or via compressed air. Will need to do both the Heat Exchanger and circuits as well as the Boiler, plumbing, valves, etc... I guess you could also grab some of the referred to Descaler above (comes in 250ml bottles too I think) and try descaling everything again then flush out thoroughly once more.

    Bit of a pain I know but nothing else for it really.

    All the best,
    Mal.
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  5. #5
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    Thanks again Mal.
    Im still a little confused though. This morning, following a 45min warm up the brew head was only just warm to touch. Upon initiating a “cooling” flush it took about fifteen or twenty seconds for any water to flow from the brew head, and the water that did initially flow out was cold. Am I correct in thinking that the HX is somehow draining empty during inactivity? This would also cause the lack of thermosyphon due to the circuit being empty, correct?
    So, what is meant to to stop the draining of the HX?

  6. #6
    Senior Member Jackster's Avatar
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    Vibe pump?
    If so, there is a one way valve in the nose of the pump. But if the water tank level is higher than the hx, it shouldn't be able to leak back.

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    Yes, vibe pump, and I generally keep the tank fairly full.

  8. #8
    Senior Member Jackster's Avatar
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    Maybe test if it's draining back into tank. Leave tank nearly empty overnight and mark the level. The hx holds enough water that if it's coming back, you will notice the level has increased.

    If it is, then test if it ever happens with the tank full.

    It could be going into the boiler, but that would have different symptoms

  9. #9
    Mal Dimal's Avatar
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    Hmmm...

    With the extra information, it could be that your Anti-Vac Valve is sticking closed such that a "False Pressure" is causing the P/Stat to operate against air pressure, rather than Steam Pressure. Might be worth checking out, clean/repair and refit or replace with a new unit.

    Mal.

  10. #10
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    Alright thanks guys, I’ll have a play around with it next week when I get a chance and report back if I find anything.

  11. #11
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    I just thought I’d share an update to this issue; whilst I didn’t get a chance to do any trouble shooting the vibe pump gave up the ghost last week. I decided to replace the one way valve on the pump at the same time, and now it appears that the thermosyphon and drain back issue has gone away.

    cheers
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  12. #12
    Senior Member Jackster's Avatar
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    Excellent result! Great to hear it's up and going again



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