As I said earlier, all three check valves in the coffee boiler path have to fail for water to drain back into the reservoir. It's possible that metal fragments from the retaining clip have lodged in the other two check valves, preventing them from functioning properly. I recommend you remove all the check valves and tubing between the pump and boiler to check for metal fragments. You can inspect the other two check valves at the same time.

Hi Dick,

I've opened one of the other check valves and it doesn't seem to have anything stuck. Meanwhile I've ordered an entire set of new valves so I'll wait for those before proceeding to remove the others.

Thanks so much for the help!

bob

Based on your experience, I ordered four more check valves (I have two on hand waiting to be installed.) My machine is 6+ years old, so I think it's prudent to swap out all the check valves. I believe someone posted here that LM is recommending annual replacement of the check valves. Probably called for at a busy cafe, but hopefully a home machine can get more mileage at $36 apiece!

I've since fixed the check valves but have another oddity at the moment..

When I run the group, the boiler pressure reads as 6bar... But i'm getting approx 440ml/min flow rate which probably indicates that the gicluer isn't clogged. On the blind however it manages to pressurize to 9bar. Coffee still extracts, but this behavior wasn't the same as before..

Have you re-adjusted the pump bypass? Instructions for doing so are in the manual. It should be adjusted to 9 BAR free-flow. When you pull a shot the pressure will rise to 10-11 BAR. That's OK because the reading is the pressure at the boiler, not the puck. The gicleur drops the pressure down about the same amount at the puck, so it'll match the free flow rate of 9 BAR.

I should also mention that if the lock nut on the bypass valve is loose, the screw can move and change the pressure. This might have happened when you were installing the check valve on the pump output.

After you set the bypass valve, tighten the nut and re-check the pressure. Sometimes you have to do several iterations to get it to read 9 BAR after the nut is tightened.

The thing is if there's sufficient resistance at the puck, or on a blind portafilter, the pressure does build up to above 9 bar at the boiler and 9 bar at the grouphead. I'm wondering if the loose circlip has somehow damaged the pump, or perhaps its another issue at play here.

Thanks for the help
bob

Definitely not normal.

Did you try adjusting the bypass valve to 9 BAR at free flow (no portafilter)? If you can't do that, then something is wrong with the bypass valve or pump. If debris got into the bypass valve then it might be compromising the spring.

I would disassemble the bypass valve and make sure no debris is lodged in there.

Otherwise, the only thing I can think of would be a leak. That would likely result in water dripping out of the bottom of the machine, which you would notice, but just in case run the machine with the covers off and make sure there's no leakage around the check valves and any other fittings you removed and reinstalled.

Adjusting at freeflow does nothing to change the pressure. It does however change the pressure on the blind. I've ran the machine for awhile now without the covers and there doesn't seem to be a leak...

I would imagine such a leak should be more obvious when the blind/puck is present, which doesn't since the pressure does go up to 9bars. I've already disassembled the bypass valve to make sure everything was functioning.

My theory is that the pump isn't functioning as well as it should, thus with the relief at freeflow it no longer can build pressure up faster than the relief from the gicleur.

Will be ordering a new pump to see how that goes. I guess it doesn't hurt to have a spare anyway.

Thanks again!
bob

Yeah, it sounds like something's wrong with the pump. The only other explanation would be a defective gicleur, such as a crack in the ruby material or a leak past its threads. But I've never heard of such a thing, so I think it's unlikely. It's more likely that a piece of the broken circlip has damaged the pump fins.