Channeling - Same spot every time no matter what

#1: Post by **deklol** » August 21st, 2019, 3:57 am

Hello homebaristas, I'm about to loose my ****. I really need your help.

My machine, Expobar Brewtus, "recently" started produce channeling when pulling shots. It is ALWAYS the same spot, 12 o'clock

First, I've googled and searched through all posts on the whole internet for people with the same problem as me ( I've spent about 14 -18 hours on this ). This has led me to test the following:

Buy other beans - Didn't help
Buy raw beans and roast myself - Didn't help
Twist the basket in the portafilter - Didn't help
Buy 2 new tampers (convex + flat) -Didn't help
Tamp harded - Didn't help
Tamp softer - Didn't help
Tamp with various different methods - Didn't help
Buy a new basket - Didn't help
Buy a new naked portafilter with a new basket - Didn't help
Put the new basket in the old portafilter - Didn't help
Replace shower screen and gasket on group head - Didn't help
Replace shower nut in group head - Didn't help
Buy a more high-end grinder (From Fiorenzato to Mazzer Major) - Didn't help
Tilted my machine forwards a bit - Didn't help
Tilted my machine backwards a bit - Didn't help
Tilted my machine sideways both sides - Didn't help
Descaling the machine and the group head - Didn't help

The ONLY thing that is making things a little bit different is when I tamp as hard as I can on the area where channeling occur and almost no pressure on the rest of the puck. The extraction is still starting in the channeling spot and will still flow more there, but not as much.

Further, I tried all equipment used (grinder, portafilter, basket, tamper) on my friends machine - NO channeling, which means the problem is not related to my technique, grinder or other equipment. So it must be produced by my machine.

I really hope there is someone out there who has experienced this issue before and managed to fix it. Please help.

#2: Post by **TomC** » August 21st, 2019, 4:55 am

What does it look like when you flush water thru the group? Has this visibly changed recently as well?

I applaud your efforts so far.

#3: Post by **dexavator** » August 21st, 2019, 7:39 am

Maybe a paper filter on top of the puck?

Victor

August 21st, 2019, 7:44 am

TomC wrote:What does it look like when you flush water thru the group? Has this visibly changed recently as well?

I applaud your efforts so far.

Good question, forgot about that. When I flush the group the water comes evenly distributed from the shower screen. Looks beautiful tbh.

Regarding paper filter suggestion:
That I haven't tried. What conclusions can I make from the result of trying this?

#5: Post by **luca** » August 21st, 2019, 8:46 am

I, too, applaud your efforts.

At the risk of causing **** lose-age, have you tried taking your basket, tamper, pf, shower screen, shower screw, gasket, coffee and grinder to another machine to see if you still get the problem there? Sorry!

Have you checked the flow restrictor/gicleur in the group head? I'm thinking that if it has only happened recently, then maybe it is scale buildup ... I know you have descaled, but I guess that could have resulted in scale dislodging and floating around somewhere. The gicleur is the narrowest part, so it's probably the part that's most likely to be affected by scale clogging, either by gradual buildup or by bits of scale dislodged from elsewhere getting jammed in it.

The other thing that comes to mind is the shower nut in the group head. Have you tried maybe loosening it slightly? Does that change the way the water flows around it?

I guess we could also check the pump. Do you have a model of the brewtus with a brew pressure gauge? If so, have the readings changed? Regardless, have you tried lowering the brew pressure a bit?

August 21st, 2019, 10:05 am

luca wrote:I, too, applaud your efforts.

At the risk of causing **** lose-age, have you tried taking your basket, tamper, pf, shower screen, shower screw, gasket, coffee and grinder to another machine to see if you still get the problem there? Sorry!

I replaced the shower screen, shower screw and gasket on my machine. The pf, tamper and grinder was brought to my friends house and produced well balanced good shots.

luca wrote: Have you checked the flow restrictor/gicleur in the group head? I'm thinking that if it has only happened recently, then maybe it is scale buildup ... I know you have descaled, but I guess that could have resulted in scale dislodging and floating around somewhere. The gicleur is the narrowest part, so it's probably the part that's most likely to be affected by scale clogging, either by gradual buildup or by bits of scale dislodged from elsewhere getting jammed in it.

Yes, when I descaled the group head I took all the removable parts apart and put them in a bath. Having descaled the machine just half a year ago and using quite soft water (with a water softener) there wasn't much scale built up. Came out as new though.

luca wrote: The other thing that comes to mind is the shower nut in the group head. Have you tried maybe loosening it slightly? Does that change the way the water flows around it?

Yes, I tightened finger-tight as per instruction when I replaced it. I could try to have it looser but...ye...

luca wrote: I guess we could also check the pump. Do you have a model of the brewtus with a brew pressure gauge? If so, have the readings changed? Regardless, have you tried lowering the brew pressure a bit?

Yes, I have the one with pressure gauge. It has been a stable 9 bar since 1.5 years back. Didn't change a bit.

Thanks for your reply and trying to help. All ideas is welcome in this situation. I just e-mailed Expobar for tips and suggestions too, so hopefully they have something they can dig out from their knowledge-base...

#7: Post by **crunchybean** » August 21st, 2019, 11:13 am

I have two guesses. First being that there may be a gasket that attaches where the portafilter seals, above the locking mechanism. That could have warped. Or maybe the occurred at the change of some sort of new technique you started doing, something like a different preinfusion technique.

#8: Post by **dexavator** » August 21st, 2019, 11:35 am

Can you post a video of the dispersion group and the naked extraction?

#9: Post by **Nunas** » August 21st, 2019, 2:17 pm

Wow, you've done everything and more than I'd have thought of. That said, something comes to mind. I think it has to be the shower screen, given the results of all your tests. Yes, I know you cleaned/changed it. Do you by any chance use an upgraded shower screen, such as the IMS? I ask because I do and have noticed something similar to what you're seeing. The shower screen with no PF runs incredibly evenly. The shower screen with coffee in the PF also runs evenly and if I tamp firmly and look carefully at the spent puck I can see a pattern on the top of the puck corresponding to the holes in the shower screen. So far so good. However, since switching to the IMS, frequently I see a little crater in the puck (this is perhaps what you're seeing). I've tried a whole bunch of things, grind, beans tamp pressure...nothing seems to be related. I've used my bottomless PF and there is no noticeable channeling. I carefully removed the puck and cut it at the hole; the hole does not go all the way through, just a quarter inch or less. I've no idea why it does this and it's not always there. It does not seem to cause any problems with the shot. Sorry, but that's all I've got!

#10: Post by **C-Antonio** » August 21st, 2019, 2:43 pm

You really bought a lot of stuff...
I would suppose you can taste that there is a problem in the coffee you get?
one thing I dont see you trying is change dose, if you do its the same thing?
When you took the grouphead apart in which conditions were the gaskets?
And you didnt tell how you preinfuse, if you do. (besides... between the two machines you tried: the preinfusion, its pressure and the point the pump kicks in, is the same? like moving the lever between midpoint and before the pump engages where water flows out and measuring the amount of water you get etc) going with the idea that preinfusion would help with channeling problems and just to make sure you compared apples to apples...

You could try limiting the flow to that area of the shower, as an experiment could be done with some tinfoil, not a cure, just to see if there is something rushing out in that position that causes it. first put the obstruction behind the shower screen, if the channeling is gone then try something smaller caught between where the dispersion screw is, 12 o'clock position.

but as a curiosity: if you noticed the point in time when this channeling started, do you remember what you did to the machine right before?