Engineer Ian here :
The thermosyphon does not go into thermal equilibrium. The machine always attempts to maintain thermal equilibrium. The group radiates heat, the boiler cools, the pStat engages, the heater adds heat, ad infinitum.

What happens is the thermosyphon gets a partial gas lock, probably from the over heated HX spontaneously flash boiling when the pressure drops as lever is lifted. If enough water is not run through the thermosyphon to expel this gas, the thermosyphon stops flowing at rate sufficient to overcome the thermal loss of the group. The machine attains a new equilibrium, albeit with a very cool snout.

It is possible to create this stall by flushing just a bit of water, when the HX is overtemp and pressurized from a prior shot. When I first got the machine, I flushed a bit to clear the screen after a shot and then let the machine sit. Drove me nuts because I could pull shot after shot with no problem

Interesting stuff, and seeing this as an issue that other users experience in normal use makes me feel a lot better.

Hm...My machine did it again today. I thought to check the output from my OPV return tube and it went down from a steady stream to just dripping. Is this indicative of a bad OPV or a failing pump?

Mike

How long since last descale?

The OPV in Quickmill machines is subject to boiler temperature water.
If the OPV has never been relubed, suspect the OPV.

Eric S. made a good point. If the boiler fill valve is leaking causing a drop in pressure to 7-8 BAR, I shouldn't expect any water leaking out of the OPV, as it's set at 9 BAR.

I recently descaled the machine and disassembled the OPV to make sure it was as clean as possible, as it was screeching. I didn't relube it. Now that I have a tube of Dow 111, I'll have to break it down and do that.

Mike

So I've been corresponding with Jim at 1st-line, who has been very helpful during this process (we've exchanged tons of emails and he's been quite responsive). I mentioned to Jim today that the scale that was on the mushroom had a light green tinge to it. Jim said that this may be mold caused by the type of water (I'm using water filtered through the GE SmartWater system in my refrigerator) and suggested I get some opinions here as well.

I associate that green tinge with the copper/brass content. Mold would have a very short lifespan at 200+ degrees Fahrenheit.

Obviously, tooooo much time on-line instead of watching the Discovery Channel
Some extreme Thermophile bacteria thrive at ideal brew temps.

BOT, the green color is almost certainly chemical and not organic in nature

Was it similar in color to this? (The insides of my Elektra hot water dispenser). If so, certainly just oxidation of the copper (which is in brass).



Mark

No, not that deep. Imagine some old-style gritty mint toothpaste. (Not gel.) Wish I'd taken a picture.