drumhead954 wrote:...a candy thermometer directly under the brew head shows between 170 & 190 degrees.
That's not very accurate. Try the foam cup technique documented in Seeking low tech way to measure brew temperature
drumhead954 wrote:I've read a good bit on the pre-extraction flush to get the temp DOWN, and that pressurized boiler water can reach temps of 235-250, so I obviously have a problem.
Actually that's only half correct; as documented in HX Love
, the flush equalizes the group temperature. That is, the HX is cooled, the grouphead is warmed, and hopefully all works out in the end.
I could be wrong, but nothing you've written so far indicates a problem with your espresso machine. If you want to post a video
of the flush, I'll be happy to provide my best guess at the end-of-flash and a starting point for pulling the shot.