Hey All, looking for second opinions from those more knowledgeable;

This morning I found my Isomac Millenium hadn't reached full pressure after being on for ~2hrs. Details:
Boiler pressure reads .5bar (typically 1 bar)
Grouphead thermometer idle reading ~196f (typically 216f)
Some steam pressure available at the wand
Pump works fine
Autofill seems to work
Red (boiler) light comes on, but seemingly only after I release steam or hot water. I can hear the boiler heating when red light is on, and pressure/temp rises to .5b/196f
Red (power) light stays on, machine seems to have constant power, reservoir is full
Green light has not come on at all
Interior of machine seems dry & quiet- vacuum breaker replaced 6 months ago
Machine was descaled 2 weeks ago

Based on all that, and some searching here, I am thinking the OPV is the most likely culprit. Thoughts?
I'm not against replacing several components if that will possibly get me back up & running sooner.

As always, appreciate the help...

I'd look at your pressurestat- it may be faulty. It's not likely the OPV on the machine, as the OPV regulates water pressure from the pump, not steam pressure in the boiler.

My first thought was false pressure, but if you've equalized steam boiler pressure by opening the steam wand, then that leaves the pressurestat. How old it is?

Thanks for the help!
Yes, I ran the steam wand for 20-30 seconds, ran water through the grouphead, and hot water tap. The steam kept coming and after all that the pressure/temps came back up to .5b/196f.

The machine's history is somewhat unknown, as I am not the original owner. I replaced the vacuum breaker, grouphead gasket, heating element seal, fixed a few other leaks, thoroughly cleaned the grouphead when I bought it in early summer. Since then it's been descaled a few times and backflushed religiously.

edit-I can try replacing the pressurestat for starters- I gather the jaeger is a worthy optional upgrade if available.

Installed a new pressurestat and the machine works perfectly now. Thanks again for the assistance!