I had the same problem. I cannot unscrew the boiler valve as well. I just cut a bigger thread (M5) and used an M5 screw accordingly.
This (especially the boiler group) looks a lot like the old Seaco Espresso machines frome the 90ies:
http://www.kaffeemaschinendoctor.at/saec...
Can you confirm that the boiler assembly is the same?
I had the same problem. I cannot unscrew the boiler valve as well. I just cut a bigger thread (M5) and used an M5 screw accordingly.
This (especially the boiler group) looks a lot like the old Seaco Espresso machines frome the 90ies:
http://www.kaffeemaschinendoctor.at/saec...
Can you confirm that the boiler assembly is the same?