Is your shower screen really clean?
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Thought I had better post this as I have taken it for granted that people make the same check as me, and it might help anyone who is not making these checks.
We all backflush reasonably regularly with cleaner (or should be) and I am sure at the end of each day, if not more often, we backflush with plain water. Also hopefully, all of us…NEVER leave the used puck in the grouphead to bake.
There is however another level of checks that people may or may not be doing. I usually drop the shower screen and group gasket at least every week and give it a clean behind there and on the underside of the group. I usually use a bit of Puly with boiling water and a group brush for this. When examining the shower screen it is easy to give it a cursory glance front and back and it all looks clean….BUT it often isn't. Hold the screen up to daylight (not room lights) and you might see a faint yellow tinge around a lot of the holes as if they have some varnish on them. In artificial light it can be hard to see. This solidified coffee residue, is not easy to clean and soaking in Puly cafe often won't shift it….especially as the Puly cools and becomes less active fairly quickly.
I find the best way, is to use some spray oven cleaner (like Mr Muscle)….leave to sit for 30-60m then scrub out with a group brush or fine dish brush….yup it can be that hard to remove. Of course remove the group gasket from the shower screen before using the oven cleaner
Why did I even check mine today…..because I was getting a little more spritzing and channeling than I should and that was the cause of the problems.