The group head (the thing that pushes water through the coffee), is a hot little beast after the machine (Expobar Office Control) has warmed up. Too hot in my unmeasured opinion. It's so hot that if you have waited half an hour to make a new shot of coffee, the water coming out of the group head will be sizzling. If you leave the portafilter off, you can see steam, bubbles, and dancing water coming out for about 3 ounces worth. So I finally emailed Expobar Australia and paid $14 AUS for a little teflon disc.
The reason the group head is SUPPOSED to be hot, is to prevent the shot water from cooling of on its way to making a good coffee. The way the group head gets hot, is that there is a "thermosyphon" that lets water circulate from the boiler to the head and back to the boiler. What this restrictor is for, is to slow down the heating loop just a little bit.
Top picture is where the top part of the thermosyphon loop attaches to the group head port, and where I planned to install the restrictor. Lower picture is the restrictor, a little teflon disc.
BTW, credit is due to http://www.home-barista.com/espresso-machines/installing-thermosyphon-restrictor-on-expobar-office-pulser-t2789.html
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