This is regarding re-furbishing a failed pressure-stat: My current Mater Elektra Semiautomatica pressure-stat had been working fine for the last 1 1/2 years - using reverse osmosis well water. I moved, and switched to Brita filter water - and 3 weeks later the stat failed. Rather than order another new one (I have a bag of stuck ones). I decided to descale this latest failed one and clean out the pipe leading into it with a tiny screw driver. (I had no pipe cleaners.)

I removed the stat and flushed it a bunch of times with a citric acid solution - (1/2 tablespoon citric acid dissolved in 5 oz. water.) I then flushed the stat with clean water a number of times. It unstuck!

10 days later my 'refurbished' Mater pressure-stat is still working. that's over 25 hours and 40+ cups of coffee. I am back using only reverse osmosis water again - no Brita. (The water here, Santa Cruz, CA may be just too hard for Brita use)

I will post when this refurbished stat fails.

Well my experiment refurbishing my dis-functioning Mater pressure stat with a citric acid descale bath ended this week after 3 months of added operation. I suppose that's not too shabby. I tried refurbishing the same stat a second time - but it did not work for more than an hour. So, I refurbished - again with citric acid (2 teaspoons citric dissolved in 5 oz water) - another used non-functioning Mater stat I had in storage. Let's see how long this other one will last. So far, it made it through today's espresso.