When you are looking at the group head thermometer, the spike at the beginning is very characteristic of all HX machines as the water at the top of the thermosiphon is at its hottest .. , but the E61 acts as a large "heat sink" and evens out those huge differences in water temps of the water flowing through it.. So your puck doesn't feel that high temp spike.. (usually that spike might go up 4C degrees on some machines).. There also will be a drop from the group thermometer to the puck.. so at the end of your shot, is your group thermometer reads 92, the actual brew water temp might be 90C.. This is because of the drop in temp as it travels through the group to the screen.. On my HX, the idle temp ends up being almost exactly the same as what the brew water will be, assuming the group is warmed up.

If you do a flush and then immediately pull, then the above is not true.. (there are 2 types of flush.. a flush-n-wait and a flush-n-go.. you can research on HB). The above is true when the group is cooler than the water in the thermosiphon, which is when you use no flush.. or you flush, wait for the temp on group to bottom out (about 1-3 minutes) and the temp starts to climb again.

You can borrow a SCACE to see the relationship on your workflow to the temp on the thermometer and the actual brew water temp or you can mount a thermocouple on the bottom of your screen as many have done. Once you do this, you will be able to characterize your machine and will only need the group thermometer.

On HX's with slow rebound, the group thermometer is necessary to tell when your thermosiphon water has reheated enough to pull successive shots.. The Appartamento is fairly quick with a 3mm restrictor in the TS.. My Profitec 500 is very slow (5-15 minutes, with a 2.5mm restrictor)