The steam boiler in one of my backup machines is in need of a descale. The anti-vac valve is off, and I can see how scaly it looks through it. My plan was to put in a teaspoon of citric acid in each day until it looks cleanish.

It's a ECM Mechanika, i.e. stainless steel boiler (but copper pipes and brass fittings).

How bad of an idea is this - will the resulting "salty" water cause galvanic corrosion?

Hi nisb

2 Tbsp Citric Acid per Liter (Quart) of slightly warmer than warm water for 20 to 30 minutes per treatment. Don't be afraid to get something long in the anti-vac valve fitting opening and stir a little every 5 minutes.

Rinse three or four times with clean water and inspect to see whether another treatment is needed.

Here's a composite screenshot "Chemical Resistance Chart" showing various concentrations of Acetic Acid (including Vinegar's 4 to 8%) and for Citric Acid. My understanding is Citric acid is also a Weak Acid (like vinegar/acetic acid) but is just 3x stronger than off-the-shelf store bought vinegar. Also, Citric acid may not be inclined to leave behind any odors or tastes in hard to remove deposits some suggest . . .

Credit: Quick Cut Gasket and Rubber Corporation

Took me at least 5 citric acid baths to get a 2 Liter Copper HX Boiler clean recently lol . . . play the long game and do several short burst descales rather than trying to let it sit too long.
(1) Testing the Heating Element to ensure its salvageable . . .

(2) After several full immersion Citric Acid Baths . . .

(3) Interior of 2 Liter boiler after several treatments with Citric Acid (the two tubes are part of the 1" diameter c-shaped HX Loop, and the small hole at bottom right is the cold-water fill line from the 2-way solenoid) . . .

(4) The Heating Element business end of the Boiler with the Heating Element finally removed . . .

(5) Before all the Citric Acid spa days, looking in through the water-level-probe fitting hole where the still locked in Heating Element can be seen complete with its coating of dark organics/buildups that coated the entire inside of the boiler . . .

(6) After two or three Citric Acid treatments, my newest acquisition off FakeBook Marketplace (a $20 1980's Dental Camera connected to an old VGA monitor) showed the truth about why just using a wrench to unscrew the heating element would have never happened. Mineral scale buildups are not our friends in these situations and several more Citric Acid baths would be needed to dissolve that mineral lock-hold on the heating element . . .

(7) After another two or three Citric Acid soaks, looking much better! (still took two or three more to get it completely mineral free, and then I finally noticed the seized-on/corroded/baked-on gasket on the outside also locking the heating Element onto the boiler) . . .

(8) A picture of the finally removed Heating Element . . . if you look closely at the lip above the threads, you can still see some of the baked on/corroded gasket that still needed scraping/wire-brushing/sanding away . . .


On a bit of a side note, I haven't really seen much of a discussion anywhere about getting a heating element free of a boiler (other than using a hacksaw and such). Here's a method but you're going to need to declare this as a hobby as its going to take some patience and time:
(1) Ensure all mineral/scale buildup is removed from the inside of the boiler. A dental camera will come in handy here for inspections of the interior of the boiler and the heating element penetration where mineral/scale build up will forbid unscrewing the heating element (locking it calcium stone coffin grip)
(2) Remove the outer large o-ring gasket completely that seals the Heating Element into the Boiler. To do this you will need a sharp dental pick (or maybe several depending on how baked on/corroded the formerly rubber gasket is). I found using an carpet knife and scraping away a little at time with a lot of force (taking care not to slip and cut myself) and about an hour or so managed to scape/cut/gouge away the formerly pliable gasket which had turned more or less to rock. You can see some of the left over gasket in the head of the Heading Element in a picture above.

It is possible to remove a very neglected Heating Element like this, but it takes patience and clearing material that is corroded and harden on. If there is mineral scale build up on the inner ring of the Heating Element penetration into the boiler, no amount of torque on the heating element will break it free . . . the minerals have to be dissolved using citric acid (possible over several treatements).

WWWired wrote:On a bit of a side note, I haven't really seen much of a discussion anywhere about getting a heating element free of a boiler (other than using a hacksaw and such).

It is possible to remove a very neglected Heating Element like this, but it takes patience and clearing material that is corroded and harden on. If there is mineral scale build up on the inner ring of the Heating Element penetration into the boiler, no amount of torque on the heating element will break it free . . . the minerals have to be dissolved using citric acid (possible over several treatements).

I have had great results removing heater elements with an impact wrench (350ft/lbs of torque) in mere seconds. I have since purchased a 'Deep' impact socket (1-7/16in) that I would highly recommend to avoid damage to both the element thread Hex nut and especially the electrical contacts.

Have you ever tried this?

. . . a fantastic post by BaristaBoy E61 above ↑ . . . and definitely underscores the importance of getting a high torque number on an impact wrench lol . . . I experimented with several used older impact wrenches before realizing that "350ft/lbs of torque" number is very much needed/important and how much newer impact wrenches have improved

With citric acid you need more attention, because in some cases it could lead to even more sustainable buildups.
Why not durgol or another liquid sulfamic acid solution? I'm using some domestic one that significantly cheaper than durgol, but with same ingredients.
If you have significant buildup in the boiler, it could persist in piping, heat exchanger, group head etc. For mechanica need to fill the water tank ~2.4l with liquid solution, disconnect level probe, open steam valve, turn on the machine and top up the boiler until that point when it starts to flow from the steam wand.
If this is a backup machine you could leave it with solution even for several hours or overnight.
Hint:
When flushing the boiler, to empty it and not make stress for the machine's pump, I'm opening both steam and hot taps, seal the vacuum breaker and using bicycle air pump pushing air into the steam wand, and all water then quickly flows through the hot water tap.