I purchased a used s-20 off ebay about a year ago and with a minor 11-month hiatus, it's rebuilt. Here are some photos before I get to the troubleshooting...

First off I tried to troubleshoot the machine before I took it apart. However, it was way too dirty. The gicars were totally filthy, just like the rest:


Even just a clean would have been worth it:


However, I called it a day and tore it apart, took at least 40 photos during the breakdown and then treated it all to a citric acid bath:


I wasn't able to get a large enough container to heat the bath in while it descaled so I had to settle for hot water. I initially stuck to a 2 tablespoons per liter of water but then found myself adding more citric acid, as it wasn't really breaking it all down within a few hours. I ended up boosting the concentration to about 5 tablespoons per liter. I know it's high but the machine was very dirty. The boiler was half-full of scale and all the tubing was filthy. I soaked everything. One quick note, the boiler used to be chromed. The chrome had started wearing off before the machine came to me but the chrome doesn't stand a chance against the acid bath. If you want to preserve the chrome in your machine, you have to descale it without exposing the outside of the boiler. Actually, I would maybe consider throwing some citric acid in through the vacuum safety valve port instead (off the top of the boiler) and using the heater to help descale in-place.

Here's an almost-stripped photo. Note, though that the groups look pretty clean, this is because I tried to clean these individually before I gave in and decided on a teardown:


Anyway, once I got it all apart, I decided to paint it over. I removed all the rust off the bottom with some sandpaper. Once it was all clean, I sprayed it with three coats of rust-inhibiting primer and three coats of rust-inhibiting paint. For a triple coat job, you'd need two standards spraypaint cans of both primer and paint. I know lots of people like powercoating and I'm sure it's very nice but I was pretty set on avoiding all costs possible. I instead spent the money on teflon gaskets for the boiler and heating element, new o rings for the gicars and group solenoids and new group gaskets. The total cost was about $65 for the gaskets.

So on to the rebuild. First, a blank slate:


As you can see, generally things are pretty clean. The frame was a bit dusty but otherwise in good enough shape. It's tough to get all the rust off around the boiler mounts but with enough primer and paint it shouldn't be a problem. Plus, I know to look out for it.


One other thing I added was boiler insulation. I bought one meter of insul-brite, the stuff oven mits are made of. It cost $9. I sewed it together and decided that all the penetrations would just be cutouts. The material is randomly weaved so it's not prone to running in any direction:


So as it stands now, I've done a bench test where I found out that the auto-fill doesn't work. I manually filled the boiler and had some good signs. First, the pump didn't want to engage when turned on, so I think the level control sensor works (a probe which I think just completes a ground circuit through the boiler). I think the culprit could be the boiler fill solenoid but I'm going to first get a multimeter and test it for changes in power to it when the boiler is full and not, then go from there. Any thoughts on this would be greatly appreciated. I get the impression that the pump works. When I removed it I decoupled it from the motor and exercised it before reinstalling. When I turn the machine on to "pump" mode, it pumps (reasonably even noise level) for a while the shuts down. Not sure what's happening here to shut the pump down, if it's not the level valve...

A bit of an update. The rancilio has two power settings. Setting one (left on the dial) turns on the pump. When I power this on, the pump runs for a while, then turns off. Then, to get the machine running, the user is supposed to go to setting 2 (right on the dial) which turns on the heat too. I manually filled the boiler to the bottom of the level probe and turned on the machine this way. As a result, I had flow through all the right places. In the manual brew mode, each group header operated well, steam and water too. I will have to get my hands on a multimeter to check that boiler solenoid. Also, is there any other way to confirm that the pump is actually pumping? I don't really know how the pump is controlled other than through level. If the machine isn't autofilling, what's stopping the pump?

Firstly, nice rebuild job.

Hopefully, you have consulted this: http://www.rancilio.com/rancilio/download_page.jsp?flag=1&id_cat=24&id_language=3 . The pump, in this situation, is typically controlled by a electro-mechanical relay contained within the "black box". This relay also typically has a clear cover so you can observe the operation.

Pressing any button other than the "continuous flow" one will time out the pump on a count of electrical impulses from the flowmeter. Pressing the "continuous flow" button will start the pump and it should continue to run until you press the continuous button again.

What makes you think something is amiss with the boiler fill solenoid?

I initially thought that the autofill wasn't working on the machine. After the rebuild, I ran the machine first in position one (which ran the pump, and I expected it to fill the boiler) then in position two, where I checked the group function. However, when I opened the boiler thereafter, it was dry. I manually filled the boiler through one of the top ports (to the bottom of the level probe) and then ran the machine on a couple of occasions to try and flush out the lines. After the machine was cool, I opened the boiler and checked the water level and it seems that the autofill is now functioning normally. I'll watch it a bit over the next week or so and go from there but as of now, it looks as if the machine is entirely functional, though I haven't brewed any coffee. I have a bit of black sediment coming out of each group header when running the machine without portafilters which I'd like to have completely flushed before brewing. One other observation, the left group, the one closer to the heater base, seems to have more steam in the group stream when running without a portafilter or coffee, but I'm not too concerned yet. With the portafilter and coffee to contend with, I imagine the backpressure will increase enough to brew well. The only thing I'm really missing is a steam tip, which went missing over the rebuild but it's an $8 part so not the worst that could have happened.

With other people doing rebuilds, how did you flush just after a rebuild? My level of sediment is pretty low, and it's definitely reducing, but if there's something I could be doing better I'd appreciate the advice. Over the next days I'll keep running it a bit and get to brewing a bit. The only other thing I need to do is to program some dosing. As it stands all the brew sizes can initiate a brew but to stop them, I need to use the manual brew button. I think this is how it's intended to go until I program the brew buttons though so no worries.

just curious how you made out on this machine, i saw one for sale that i have been eying, the wiring harness was chewed up by god knows what in storage so its a good price.

I've got an old S20 Midi CD, (so like yours, but without the coffee dosing control). - It's doing the same thing; not filling with water, and I thought it was the fill sensor too! I know they're a replaceable part because I've seen them for sale.

For a long time it worked fine, but just recently it seems to have stopped filling the tank. - Every now and then I can get the pump to come on, but it doesn't stay on long enough to fill... then it goes over temperature and turns off.
The fact I can get (cold) water out of the heads suggests to me that the pump is working. However if it can't tell the tank is empty, it will never know to put more water into it.

It sounds like you got yours working again by giving it a jiggle. Any tips for me?
I know I should just man-up and take the thing apart to clean it like you have, but I'm still a little unsure of what I'm doing inside the machine... and it already gave me a belt when we took it apart to do a clean on the frame etc.

Sketcher, I took a look at the manual for your machine and it works like many Simonellis of the same age. The boiler fill valve will open and the pump will activate for a specific period of time (usually 20 seconds), after which it closes automatically. The autofill feature of this machine is not to fill the boiler from empty, but to adjust the level when it is already filled to the proper amount. There should be a manual fill switch, or a ball valve under the drip tray to let water into the boiler using line pressure.
I could be wrong, as I have never worked on your machine.
You can test the functioning of the solenoid several ways. First by taking it apart and making sure that everything is clean inside the valve and the seals are good. Then testing the coil with a multimeter. Or you can also hold a screwdriver to the tip of the valve (where the nut holds the coil) while it should be active. If there is a weak magnetic pull, the coil is usable.

Hope this helps.

Troy