Highly variable pump pressure

[brandon]

http://www.youtube.com/watch?v=vZsjp8rQOeM

I posted this in Home Barista as well but decided to take a video so people can hear/see for themselves. Basically when I start running a shot, the pressure ramps up as usual to 8-10 bars, but it then drops off significantly in the 5-6 range with the pump becoming much quieter. This pressure oscillation and sound changes continue throughout the shot.

I've had this problem for a couple weeks now. I notice it's been accompanied by some pretty bad channeling problems (I've tried recalibrating grind and changing coffees -- right now I'm grinding ~20-21g in 15-16 seconds on my Vario, so I'm pretty sure it's more or less dialed-in), but I'm not sure if the pump pressure changes are causing the channeling or if the channeling is causing the pump pressure to change -- or maybe it's a complete coincidence. In any case, the channeling in the video isn't that bad (it's dark, I know) but the pump pressure is still changing.

[chas]

If you have one of those in tank softener filters, the first thing to try is taking it out.

[brandon]

That's with the filter already out.

One thing I've learned by now -- taking the filter out is the first step to fixing any problem!