Story:
I use a mix of about 2.75 gallons of reverse osmosis water with a quart of Brita-filtered water added. After approximately 20 months of daily use I decided to my first descale of my VBM DS manual, as a preventative measure. Over this period I had removed the mushroom a few times for examination and only once did I find any buildup of scale. Even then, it easily wiped off with a towel, the build up being more of a thin surface layer than a hard layer of scale. With the exception of two or three already-reported thermal stalls on occasion, the machine's performance has been fine.

The backflush was done with Urnex Dezcal, mixed at the lower concentration recommended on the packaging (one, 1 ounce packet in one quart of warm water). I let the solution sit in the boiler and HX for about an hour, and when it was flushed out there was virtually no difference between what went in to what came out. No evidence of scale build up and the agent was very clear. After flushing out with less than one reservoir of clean water the rinse water from the brewhead as well as the hot water tap was tasteless. I even disconnected the water level sensor so the boiler would completely fill, just like the excellent instructions mention .

Problem:
The machine is equipped with Eric's adapter and now, after the descale, the brewhead is heating very slowly when the machine is turned on in the AM. Before the descale, the temperature readout after about 30-45 minutes would read around 207 and when given a cooling flush would hit around 210 or so before dropping down. Now, after idling for around 40 minutes the temperature was around 160-170, and even after nearly an hour the readout was under 200 and it took a few flushes to get it over 200, and it only flushed up to about 207 or so. Brew temperature is normal, but it took that hour of warm up to get enough heat into the brewhead for brew temp stability. So looking at that I would guess that it is showing signs of a thermosyphon stall.

I put a thin-wire thermocouple in the flow from the brewhead and the temperature of the water coming out was close enough to that of the digital thermometer that I do not suspect thermometer error as the culprit. ADDED: I also did a few blind filter clear water backflushes to see it there was an obstruction that might be cleared that way, but it made no difference.

I was at a stalemate, so I took the brewhead off the machine this morning. I put a hose on one of the thermosyphon pipes and blew into it and found the flow to be fine- no restriction whatsoever, and there was a puddle of water in the open drawer to prove it! [note to self- put towel in front of water pipes when testing.]. The inside of the thermosyphon pipes were completely clean and free from any signs of scale. I pulled the water level sensor and it looked new with absolutely no sign of scale or corrosion. I pulled out the thermometer and its shaft was sparkling clean and the passages are clear. Other than a darkening of the copper pipes, all those parts looked virtually new.

Brewing performance in terms of water flow is fine as is brew pressure and boiler pressure, and the pressurestat is operating properly, cycling as it always has. Steam performance is fine as well.

I took photos of all this, just in case, but there is nothing to see. The mushroom is the only part which shows signs of some chrome wear and such, but this has been progressive and not part of the descaling process. The thermosyphon chamber of the brewhead looks very clean.

My first thought was that the thermosyphon restrictor was clogged from some floating debris after the backflush (did you think that as well?). We were wrong. I pulled it out (located at the boiler end of the upper thermosyphon tube) and it is sparkling clean and free from any sign of constriction and it is the .11 size as stated in other posts here on HB.

At this point I am thinking, "two thermosyphon stalls in a row...???"

Is there some place in the brewhead of which I am unaware to check? I removed the thermometer mount and blew through the drilling and it was fine.

ADDENDUM: After I got it all put back together and used a blind filter to test for leaks, I let it idle for about 30 minutes and it is now (seems to be) working properly, coming up to a 'normal' temperature, of course, and for no good reason at all other than the threats I muttered under my breath during assembly..

I think you've got everyone stumped. The only thing I could guess is an obstruction, bubble, scale, ?, in the thermosyphon return line. The fact that it cleared itself (or was driven out by harsh language) makes more frustrating.

Randy G. wrote:After I got it all put back together and used a blind filter to test for leaks, I let it idle for about 30 minutes and it is now (seems to be) working properly, coming up to a 'normal' temperature.

Espresso gremlins. Mock the idea if you dare, but they're real.

Is it just me, or do many report problems after a de-scale? It makes me quite nervous to do one?

The descale had absolutely nothing to do with it. While I was chasing the caffeinated gremlin that caused the perceived problem I pulled the water level sensor out of the boiler and peered in with a bright light. The inside of the boiler looked new. All the piping I examined looked new. The flow restrictor looked new.

The idea about descaling is to do it before it is a problem and before the scale gets heavy. This extends the life of the machine, but mainly the heating element. It also helps maintain proper water flow.

There is far more danger to the machine from not descaling than there is from doing it. I can say that the Dezcal took less flushing to get out of the VBM than the citric acid I used in Silvia.

Of course, the best thing is to use water that lessens scaling as much as possible. What I have been doing evidently works in that regards.

But why would I get two thermosyphon stalls on consecutive days? The one on the first day was extremely difficult to overcome. I flushed, waited, flushed, waited, and even after nearly an hour it was still not up to temperature.

But everything seems OK now. I ran the machine twice today, allowing it to cool between and it came up to temp fine. I wonder.... Maybe the machine is pointed in the wrong direction... Forget the PID.. I am going to equip my VBM with WAAS enabled GPS.

EricL wrote:I think you've got everyone stumped. The only thing I could guess is an obstruction, bubble, scale, ?, in the thermosyphon return line.

My thoughts were along that line. Air bubble came to mind, and it would not take much to cause a blockage in the gicleur/flow restrictor although I saw nothing that would point to the later. I even removed the restrictor and it was clean and clear. I even put a hose on one HX tube, blew into it (not hard) and water shot out the other tube. then reversed the process and both tubes were unrestricted. The tubes are quite large in diameter and a lot of water came out with good trajectory.

The only explanation I have is thermosyphon stall. Two consecutive days- lucky me. The good news- I now know the insides of my machine even better and it is nearly clean as new. About the only thing left is to keep an eye on the mushroom and when I get a chance I will probably remove the rest of the chrome from the mushroom just to be sure it is not a cause of future problems.

One suggestion
regarding this and why other machine grouphead that has one:
after a descale always remove the gicleur
and clean it soaking it in solution on its own
then re-install it
adds only couple of minutes to the job

stefano65 wrote:One suggestion... after a descale always remove the gicleur and clean it soaking it in solution on its own

That's good advice because I would assume that some machines with sufficiently large plumbing (like the VBM DS) with a clogged gicleur can still exhibit correct flow rates in use but will not properly thermosyphon and so will result in low brewgroup temperatures and thus low brew temperatures. Descaling can loosen larger bits of scale which do not dissolve and these can be easily caught in the gicleur's small orifice.

I suspected this as well, so I did remove the gicleur after descaling and it was perfectly clean like the rest of the machine. I even passed the smooth end of a drill bit through it.

And I can report that the VBM performed perfectly this morning (Sat., 2/21).

Hi Randy, seems similar to the problem that I had, which disappeared and then haunted me once more. Removing the OPV and cleaning it up seemed to fix it the last time around.
Cheers,
K

buzzmccowan wrote:Hi Randy, seems similar to the problem that I had, which disappeared and then haunted me once more. Removing the OPV and cleaning it up seemed to fix it the last time around.

I checked that out... Out of paranoia as much as anything else, I removed the mushroom and took off as much of the chrome as I could. If they insist on chroming these it should be hard chrome, nickel, or something that is going to stand up to that environment, or not chroming it at all. After only 20 months the chrome on mine looked bad. I took the top cap off and examined the gicleur *1 and it looked excellent and the four holes in the mushroom were all perfectly clear. I then removed the piston of the OPV and it all looked clean as could be. No scale, no particles, nothing of note.

The next suspect is the piston seal of the OPV. over the next few days I will try removing the return hose from the reservoir and see if that is leaking while the machine idles and will do the same with the drip tray, emptying and drying it to see if the group is leaking.

After all that I think it's time for chicken bones and the mojo hand.

*1 - I had some confusion. The gicleur is a small orifice, like a carburetor jet, screwed in the top of the mushroom, located under the top hex cap bolt on the group . It is protected from clogging by a stainless steel filter screen. The flow restrictor in the boiler end of the lower thermosyphon line is a different part. And just to clear things up, I have removed both for examination and those were not the problem.