Direct me if I am wrong, but I did a search & did not find this topic already.

At my work we have a 2 group Rio, each group seems to be completely different.  Pulling two basically identical shots each weighed & tamped equally there is ~10 to ~13sec difference.  So if we dial in for one side the other is horrible, the is no happy medium.  Any advice or tips would help.  A coworker recently took the machine home to descale it, found hardly any buildup in boiler, it had not been descaled in ~6 years.  He mentioned it had massive amounts of buildup on what I assume is near the group ( I am not familiar with the inner workings at all! )  It has become really frustrating, the groups have always had a slight difference but this is awful.

-please help

+ thanks much

- I will try to get more info together possibly some pics

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You probably have an obstruction of scale somewhere in the slow group's water pathway. You can verify this by running both groups without a portafilter in place for 10 seconds or so, catching the water in identical cups, and comparing the amount of water you get. You'll generally see a little difference, but my guess is that you'll see a more pronounced difference.

Most machines have a smaller orifice somewhere in the water path to control flow. There's often a metal screen in this area as well. Both have likely picked up a substantial amount of buildup. The problem is hopefully isolated to just this orifice and screen but may involve a couple of the pipes as well. I'd plan to have both of the orifices and screens cleaned and/or replaced. Sometimes the group's internal flow paths will need to be reamed out with a drill bit as well.

This is a pretty involved repair, and not one that I'd generally consider to be a DIY job. This is one of the reasons that proper water conditioning is so important for commercial machines.

Good luck.

To clarify a bit more - make sure you replace the screens and orifices on both groups. Even though you clearly have a slow group and a fast group, the fast group probably has some obstruction as well. If you only replace the slow one, it may become the fast one and you'll be in the same place. Best do both while you're in there.

Not sure where this obstructed orifice might be located on the Rio. There's sometimes one in the group itself under a large hexagonal cap, though it might also be in one of the flowmeter ports. It's different for Astoria vs Wega (other CMA-made machines).

It sounds like Brady hit the nail on the head.  We are having a similar problem right now with our 3 group GB5.  It's a real pain.  Luckily 2 groups still function properly.  Definitely clear our both groups at the same time because we have also had the slow group become the fast group when clearing out only one at a time.  Brady, here is a tough question though.  The middle group on our GB5 is pulling slowly but is flowing fastest with an empty portafilter.  The shot starts out fine but then slows way down after about 10 seconds.  It pulls real slow, like a trickle and then speeds back up, finishing 6-10 seconds behind the other 2 slower flowing groups.  I'm stumped.  What in the world could be causing this? We change our filters regularly (every 400 gallons or so) but are learning that's not quite regular enough.  Man the freakin' water sucks in Florida. Hope I haven't strayed too far off topic.  If so, please ignore me.   

thank you for the speedy reply, I'll toss the info into the mix at work & possibly might post with more details. you are awesome.

Brady said:

To clarify a bit more - make sure you replace the screens and orifices on both groups. Even though you clearly have a slow group and a fast group, the fast group probably has some obstruction as well. If you only replace the slow one, it may become the fast one and you'll be in the same place. Best do both while you're in there.

Not sure where this obstructed orifice might be located on the Rio. There's sometimes one in the group itself under a large hexagonal cap, though it might also be in one of the flowmeter ports. It's different for Astoria vs Wega (other CMA-made machines).

Any luck figuring this out?

While this sounds like it is probably a water quality issue, the more common cause for this problem is that the screens and baskets are worn.  Often, one group gets used more then the other and that side pours faster.  Or one group has a newer basket and the other has an older basket.  Best practice is to change these parts out as sets, and don't keep old parts around.   I've had many calls for this issue over the years, and most of the time it is due to mixing new and old baskets and screens.  Hope that helps.

so... the latest update i received from coworker...

he took it home again over labor day weekend, descaled all pipes/ innerworkings i assume, now both sides are running strong!  In his words "the slow side was 80% blocked & other "normal" side was about 50% blocked".  Now both sides are running pretty much even, & WOW I have tasty espresso now, the machine seems to produce a creama now much thicker than before.  This is a very neglected ( maintenance wise ) machine, for atleast ~6years.  I'm not sure what else he has planned for machine but regardless I have good coffee>>>>finally.....

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