Thursday, 18 August 2011

Mini Vivaldi Brew Boiler Descaling

I started this overhaul with the intent of getting inside the brew boiler to see if any scale had built up over the last 2.5 years.

After about 1.5 years, I added a descaling solution to my reservoir to descale the brew boiler, but since I can't see inside, I was never sure it removed everything. At the same time, I inspected my steam boiler by removing the vacuum breaker and looking inside with a flashlight. Everything looked clean there, but since I use the steam boiler only on demand, the brew boiler gets about 10 times the use (or about 2 hrs per day using my timer).

The first step to opening up the brew boiler is to remove the large lugged brass nut. You could use a "adjustable hook wrench" if you happen to have one for adjusting motorcycle shocks, but since I didn't have one, I simply used a piece of wood and hammer to get it turning. The wood helps prevent breaking off a lug if hit directly with a hammer. I could have also wrapped it in a towel and turned it with a large wrench, but there is not much room so the the wood piece seemed like the best method(which worked very well after a few light taps).

The nut came into contact with the heater tabs near the end of turning, but the tabs bent outwards slightly and the nut came right off exposing the back plate of the heating element. The back plate was still stuck against the boiler, so no water came out, but I put a yellow cup just underneath for when it started flowing.

To get the heater out, I needed to pry the backing plate away. WARNING: There is a small anti-rotation pin on the backplate, so don't try twisting it off. Instead I found another method that work extremely well. I took an old chisel and tapped down lightly into the gap at a few loactions to gently pry and work the plate away from the boiler (and the water started coming out like CRAZY). Next time I do this, I'll roll the machine onto its front at this stage (before removing the heater element). That way, the water will stay in (until I syphon it out), and descaling will be much easier as well.

There is a black o-ring in a groove on the outside edge of the back plate as seen in the photo below. So be careful not to cut it if you use the chisel to wedge the back plate away. Also, don't use the chisel from directly on top, since you might contact the small anti-rotation pin inside.

Once the heater breaks free, the water begins to come out (so be ready with a big cup....bigger than the one I have here... which overflowed).

NOTE: For re-assembly, it's a good idea to lube up this critical o-ring with Dow 111 food safe valve lubricant & sealant which you can buy from Doug & Barb at Orphan Espresso:

What came out of the boiler was a TOTAL surprise. I expected clean water like I found in the flowmeter, but instead I found a gross, milky water with small white particles floating around.....YUUUUCH!

What is this stuff you ask? Scale? Nope... I had seen this once before when I had changed my filter. This is the stuff that comes out of the water softener cartridge after it's used for the first time. I had just installed a Rancilio Silvia softener, and the resin (which is coated with NaCl for ion exchange softening) will appear cloudy like this at first use. I'm pretty sure it's not dangerous, but none the less, it looked totally disgusting.

Now how about inside the boiler? Well here's what it look like as I first opened it:

There were a few white lumps (scale pimples?), mostly on the stainless forward section of the boiler (not the copper back section). There were a few bigger soft lumps, but I assume this was softener resin. Whatever the large lumos were, they came off rather easy. The smaller bumps were harder to remove.

The the inside neck of the boiler (just inside the threads), appeard to be corroded at the bottom (as did the backing plate). The nickel plating had been eaten away, exposing the bare copper, but only at the bottom. I had seen this in photos of other machines that were stipped for descaling. My guess is that the heating element falls slightly when assembled and makes a light "point contact" between the brass backing plate and nickel plated boiler wall. This combination of water, metal, heat and charge seems to produce the perfect galvanic couple to produce corrosion. SO BE WARNED: For this reason alone, I'd recommend opening the brew boiler like I describe here every 2 years maximum, to check the conditon. When I re-assemble, I will likely lift the heater up before tightening the nut to see if this doesn't prevent the contact at the bottom.

The heating element had a thin, white layer of scale started. Not much. But enough to do some descling using a citric acid solution (1 teaspoon of citric acid powder for 1 litre of water).

After a 30 minute soak, it came out pink and perfectly clean.

I dipped a scotchbrite scouring pad into the citric acid solution and used this to scrape the inside of the boiler clean. I stuck it on the end of a wood rod to act as a handle since my fingers were not long enough.

After a bit of scrubbing and soaking for about 30 minutes, the insides were sufficiently clean (though not perfectly smooth). I thought about tipping the machine on its front and filling the brew boiler with citric acid, but the result I had with the scouring pad seemed good enough.

I then removed the vaccum breaker from the steam boiler and poured the remaining citric acid into the steam boiler. I removed the citric acid after 30 minutes using the "syphon method" shown in the photo. If I had a drain plug on my boiler like on the newer Minis, I would have used that, but the syphon works just great.

One other thing you might notice about the steam boiler from this photo. The flimsy, paper thin, white plastic boots on the wire terminals have all discolored to yellow from the heat on top of the boiler. (They are still white on the sides where it is cooler).  A very poor choice by the engineers on such an expensive machine. If I can find some higher quality "clip on" replacements that will withstand the temp, I might change them.

I'm now ready to puit everything back togther. Nothing special here so I won't bother posting photos (unless something interesting happens).


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  2. This post is really nice. At first time I can saw the inside picture of the boiler. But I just want to know the boiler replacement process .

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