Greetings Espresso Lovers
I have a plumbed in Pro 700, and recently the brew pressure gauge which had been reading a rock solid 2 bar has been reading 10-11 bar during warm up and at idle. Gauge reads 2 bar when off, and my pressure gauges downstream of my pressure reducing valve has also remained steady at 2 bar.
When on and at idle, I can lift the grouped lever and drop the pressure back to 2 bar immediately, but it will then begin to slowly climb again.
It does stabilize when either of the boilers are heating. Im running my steam boiler right at 1.5 bar (I dont have the pressure upgrade) and my brew pressure is set on the pump to give me 9 bar.
Im guessing one of my check valves is not seating properly (and possibly a solenoid valve seat), but even if my steam boiler was leaking back, it shouldn't be allowing my brew pressure gauge to be climbing to pressures in excess of my pump output pressure.
Any ideas/thoughts?

See my general comment from Faulty pump pressure gauge?

HB wrote:The pressure reading when the machine is idle isn't important.

To elaborate, pulling a shot introduces cooler water into a closed system, but then you suddenly close off the main exit at the end of the extraction. As the water in the boiler warms up, it expands and the pressure rises. The expansion valve is typically set to open around 12 bar for rotary pump espresso machines since they have their own bypass valve to regulate brew pressure. For vibratory pump espresso machines, the expansion valve (traditionally called an over-pressure valve in this context) is set to open at the desired maximum brew pressure, usually around 9 bar. This valve vents water into the driptray to avoid subjecting the hydraulic system to excessive pressure. It only needs to let a few drops of water escape to reduce the pressure sufficiently.

What you describe above sounds normal to me.

Hi Dan, Thanks for the input. The brew pressure gauge is just on the outlet of the rotary pump, with check valves downstream of it.
The machines never done this before, whether it was using the integral tank or plumbed in. Just started a few weeks ago.