Referring to valves with specific names can confuse people further.wlaughto wrote: Also just for clarity, the Over Pressure Value (OPV) you are referring to here and have hilighted in the photo above is a different OPV to the one on top of the boiler? When I Google Over Pressure Valve posts point to the one on top of the boiler.
The one below the reservoir in your machine is the expansion valve, it is there to allow water to escape the closed heat exchanger circuit when the machine is heating. It is an over pressure valve and also works to limit the maximum brew pressure because the machines with vibration pumps don't have pump bypass relief valves on their pumps.
The larger of the valves on top of the boiler is the safety valve, it too is an over pressure valve and it's there to release boiler pressure to atmosphere before the pressure gets high enough to blow the connectors out of the boiler if the heating circuit fails and heats non-stop.
But, yes. It's the expansion valve that is limiting the maximum pressure in the brew circuit while the water is flowing. Adjustment of the expansion valve is done by removing the cap (Where the flexible hose is connected) and turning the valve inside with a large flat screwdriver, either tighter against the spring (Clockwise) to increase pressure up to 10.2 bar or so, or counter clockwise to bring it down to 10.2 or so.
And Kitt, awesome, thank you for offering to help. knowing that the pump is working well against 10.2 bar would make the troubleshooting easier.