My Linea Mini used to idle somewhere between 6 and 12 PSI. Recently, after brewing and during idle it goes to just slightly above 0. Brew pressure when brewing is exactly 9 PSI.

I've tried adjusting the expansion valve but it doesn't seem to have helped. Do I just continue adjusting it until I see some change in the gauge after brewing?

Also, the drip tray is filling up much faster and it is using a lot more water than usual.

Thanks for the help.

Don't know about the mini but ignoring brew pressure gauges while not brewing is a general rule of thumb for espresso machines.

Edit, not sure which gauge you mean. The boiler pressure for the steam? Do you have steam pressure?

Steam pressure is normal. At first I thought it was time for a new vacuum breaker due to the high water usage. Then I started to notice the brew pressure gauge acting strange.

if your tray is filling, your vacuum breaker valve is leaking by, which is probably why pressure is dropping. You can open the breaker valve and clean up the residue and scale and that might work at getting it to seal again. If you have the new style GS3 breaker (black plastic thing), see if you can get the old style brass ones. They are cheaper and can be rebuilt. I have found with mine that the o-ring is usually what needs to be replaced and you can pick those up very cheap.

The vacuum breaker would have nothing to do with an idle pressure of zero.

The leak is your 3 way valve.

See here:
La Marzocco Linea Mini Leaking After Plumb In

Thanks for the link. Indeed it does seem like a 3 way valve problem.

Has anybody had luck just cleaning it or does it typically require a replacement?

Always worth a cleaning cycle with cafiza or similar.