Max1411 wrote:An extremly effective way in heating up a E61 HX faster is by emptying the whole upper thermosiphon.
I've used Max's method at times to get a rapid heating in my old ECM Giotto and newer Rocket Evo. Beware, It can get the group really hot! - I've gotten as high as 220F on the grouphead thermometer on a machine that normally idles at around 203F.
I've toyed with it as a way to get faster temp rebound after pulling shots in succession but haven't perfected it for that. It's easier to just be patient and wait for the group to slooowwwwly come back up to around 197F and pull a shot with just a very brief cleaning flush.
It makes sense to me that it works. If you get a little vapor at the top of the TS loop, that breaks the siphon and the group goes cold because TS water is no longer circulating. But if you drain down the group a lot, then the top of the HX and TS loop is all vapor, and steam generated in the HX will rise to the top of the loop and condense, with most of it draining back via the bottom TS tube. The heat transfer here will include the heat of condensation in going from steam back to water, which is huge compared to what you get from cooling water in a proper thermosyphon.
Max1411 wrote: I don't know how it works with those machines having a immersion tubing at the HX outlet like the newer ECMs and Profitecs.
Yes - I expect it would be less effective on those machines that have a plastic tube extending from the upper HX fitting down into the HX chamber to pick up water nearer the end of the injector tube.