I am looking for a plan to draw down the temperature that heat exchangers store between brewings.

I am trying to nail down a routine with my Expobar Office Control, a heat exchanger. It's an automatic, but I always use the manual brew button so I can shut off the pour when the color starts to change. I've read a lot about temperature surfing with Silvia, but that is not a heat exchanger, and I don't have separate hot water-steamer switches that the online method says to use. My machine only has the hot water knob for drawing hot water, and the steam knob. No pressure or temperature indicators.

I am not sure if the right method is to run water through the grouphead, (then the red light goes on) and then wait 20 seconds or so (my red light goes off after only a second or two), and then put the loaded PF in. Results are not inconsistent! All my other variables are stable--grinding, packing, tamping, etc.

Any help appreciated!

Have you read Managing the Brew Temperature of Heat Exchanger (HX) Espresso Machines? The Expobar HXs run hotter than most and I recommend a short rebound (10 to 15 seconds).

You could also put a flow restrictor in the thermosyphon line. Kind of like a rubber washer with a smaller hole in the center. It reduces the flow rate through the group, keeping it cooler at idle.

Depending on how much steaming you do, you could lower the boiler pressure substantially.

On my big machine, 11 liter boiler, I ran the boiler at .8 bar and still had more than enough steam thanks to that huge boiler. Even at .8 bar, the group will still get quite hot. .8 bar is still 242.9F, .7 bar is 239.7F. Still way above the 195-205F brew mark. You can go lower but as IKE points out, you will have no steam to speak of.