are you heating the citric acid in the boiler or simply letting it sit.
I had a problem descaling with citric acid a month ago: using it worked good on the boiler but clogged my pstat

anyone else experience SLIME?

could it be ORGANIC?

Sometimes coffee can get back into a boiler if the piston seals are degraded. You could try using a coffee detergent like Pulycaff to clean it taking care not to overheat and cause a foamy mess.

I suspect the black slime is cupric oxide. It can look slimy when still wet. It's a protective coating that can form naturally on copper.

If so, do you think a detergent would leave it alone?

Not sure. Here's another time when we miss Dr Pavlis dearly...

In my experience, even if you descale and strip it away, it returns fairly quickly. I have no understanding of the science behind it but it seems to persist in certain environments. It is present in some boilers of my machines and not others.

But it's a beneficial, protective coating that is naturally occurring so there's no reason to remove it if there is no scale present.

whatever it isit didnt just FEEL like slime. I was able to easily wipe a mucousy slime off the lower boiler with a paper towel.

grog wrote:Not sure. Here's another time when we miss Dr Pavlis dearly...

In my experience, even if you descale and strip it away, it returns fairly quickly. I have no understanding of the science behind it but it seems to persist in certain environments. It is present in some boilers of my machines and not others.

But it's a beneficial, protective coating that is naturally occurring so there's no reason to remove it if there is no scale present.

This^^^

If Dr. Pavlis were here, I'd give more than a penny for his thoughts on this. Nevertheless, I feel he left us a lasting legacy, words to live by if you will. My takeaway from him has been this:

1) If you use scale free water, you will not (cannot) develop scale. I do this, and I do not descale. It is simply not part of my thought process.
2) If you add a little potassium or sodium bicarb to your distilled water, your pump machine sensors will work right, and your wetted brass and copper will like it. (One of my pump machines has stainless boilers... I have no idea if there is benefit or null, to using "Pavlis water" in it, but I do anyway.) Of course I use "Pavlis water" religiously in my Pavonis.

So if I have that black slime, (and I don't know if do or not), I'm not worried about it... Not enough to clean it off.

I have two latter day Pavonis. A 2000, pressurestat, single power switch, pre-Millennium, AND a nice 2012 Millennium, that I put in a joke offer of $240 for on eBay shortly after Christmas a few years ago, and somehow won it. I don't use the Millennium that much, but as a Pavoni fan, I like that I have it. Anyhow, I think both these machines have chemically similar construction.

-Peter

Yes prevention is better than cure but still, I have black slime and am thinking it is organic material and that so few others see it happen