As mentioned in my other post the 3 way exhausts continuously whilst brewing.
That should be fixed FIRST
- oftentimes you can purchase simply the internal piston if $ are short but I would opt for the valve assembly less solenoid.
In lieu of this pressure limiting valve, you need a pressure regulating valve. This is a good choice - https://www.watts.com/pages/_products_details.asp?pid=3428
in the 1/4" size.
Disconnect the pump electrically, hit the brew switch, and adjust the regulator such that the machine's brew pressure gage reads 2.25 to 2.75 bar. 2.50 bar is nice but it doesn't need to be exact.
Reconnect pump. Install a blind filter and "brew away". Adjust the pump's pressure regulating such that your brew pressure gage reads 12 bar. Now adjust the expansion valve (maybe that's what you're calling the retension valve) such that it is slightly
dripping into the box while the pump is running.
Let the pump cool off for a couple of minutes - even rotary pumps have an overtemp breaker. Restart pump with the blind filter in place and adjust the pump's pressure regulator such that the brew gage reads 9.0 bar or wherever you would like. Remove the blind filter and simply flush water through the group - the gage should read 9.0 bar - adjust as necessary.
The reading on the brew pressure gage is, for all practical purposes, MEANINGLESS
unless you are actually brewing coffee - as Dan explained