I am looking for advice on what I should check, replace, clean, etc. to fix our machine. Any help is greatly appreciated. Local Mom & Pop coffee shop in Mobile, AL.

The machine in question is an CMA Astoria Rio, 2 group, single boiler, HX, rotary pump, plumbed in espresso machine.

The dispensing pressure gauge, when not in use, reads 5 bar (good) and when dispensing button is pressed, it randomly reads 5 bar or at any time in pulling the shot may shoot to 9 bar. It is random with every shot pulled with the pressure jumping from 5 to 9 chaotically during dispensing.

I checked the dispensing pressure gauge with mains off and on and it reads correctly. The boiler pressure is normal. The boiler interior has very little scale but, there is a crusty build up on the exterior water supply fittings to the HX. The water supplied to the machine is filtered (3M cartridge system).
Other items of note; the dispensed volume of coffee from the left side group is larger than the right side group by 4 to 1.

Thank you for your time and I appreciate the help.

Brian

The 4:1 difference in brew volume is an indication that things are not right inside your machine. The scale buildup on the HX fittings indicate there is likely scale buildup inside your machine. How do you know your boiler has little scale in it? Where you able to get a visual of the inside? There might be significant buildup in the HXs, or in the tubing to/from the HXs, and in the passageways in the group head.

Something is not right in the pressure dept, as well, as indicated by the gauge. Either the gauge is wonky, or there may be issues with the bypass valve in the pump (they scale up, too).

How mechanically inclined are you?

In regards to the boiler I removed the heating element and shined a flashlight inside and there was very little scale build up on the walls I estimate half of a millimeter at most. I agree that there may be more build up in HX but, no verified observation. I checked the gauge by turning the main water supply to the machine off and the gauge read zero. I then turned it on and it was back to 5 bar. I am fairly mechanically inclined and the repairs I have done in the past on this machine were replacing sight glass assembly and steam wand assemblies. What did you have in mind? Thanks for the response and look forward to your ideas.

B