Can anyone help me figure out my Rancilio L4 channeling problems? I use a bottomless portafilter and have become annoyed lately at not being able to pull a quality shot mostly because I experience significant channeling. I have tried various grinds, tamping techniques and adjusted the machine's pressure up and down with few changes in the amount of channeling. I keep the group head and the rest of the machine clean.

I believe the machine works as it should but would likely benefit from some maintenance. The wire insulation and connectors are brittle and appear their age. I use soft water but haven't inspected or cleaned the inside of the boiler or the machine's copper plumbing.

I am interested in what service, maintenance or rebuilds somebody might suggest.

I read through the three pages ref an L4 but had so start a new thread because apparently the thread was too old to post too.
Rancilio L4 - Adjustment of Pressure/Temperature

Thank you.

Channeling is most likely from grinder and prep issues. What grinder are you using and how do you prep your basket?

I use a self-refurbished Rancilio MD-50 grinder. My channeling occurred before I replaced the burrs and after. It also happens with grind from my local coffee shop. I am fairly convinced that my channeling is not associated with the grind. I have tried many techniques as far as prepping the basket, also without changing the channeling. I have experimented with grind, distribution and dosing without channeling improvement. These two links seemed helpful, but didn't change my results.

/naked-extr ... usion.html

Weiss Distribution Technique - Step by Step

Tinkering with the L4 some more, I switched the pressure stat wire to the third and last "new" contact, and decided that I would throw some parts on. I ordered a "Rancilio 'Epoca' Water Level Adjustment Pressure Switch" from espressoparts.com to replace the type 760 pressure switch that rattled a bit when I removed it for cleaning. I also ordered high temp silicon wire, spade terminals and terminal protectors to replace the original wiring. All should arrive within a week or so.

Now I need to decide if I should disassemble the boiler and plumbing while I am in the maintenance mode.

Can anyone recommend disassembly or not? I am not interested in breaking things for no reason.

Thanks.

This is what it looks like inside,

So it goes... I have a few days before my parts arrive and decided to disassemble the boiler. I am glad I did, although unfortunately I did not capture the ugliness in photos. Black flakes and chunks filled the bottom of the boiler, and green and silver tarnish covered the side and the HX tube. Several cycles of vinegar, citric acid, walnut shell blasting and steel wool rubbing over several days took care of most of the undesirables. I've determined that some of the intrusions will not come off, at least by me with my inexperience. Does anyone have suggestions?

Boiler pix coming soon. This is my HX tube after several days. The blueish green tint is actually silver in real.

The final bath, a citric acid filled boiler.

Thanks for the input. My L4 has a vibrartory pump not a rotary pump. I am not sure if it was designed to pre-infuse, but I see an initial spurt of water, a slight pause, then continuous flow through the group head without a portafilter attached. Prior to my current disassembly, I experimented with low dosing and had the same channeling as with my normal 21g dose. I hope to have her going within a few days.