I'm repairing an Isomac Tea Cool for a friend, about 10-11 years old (the machine that is).
It was never cleaned, so everything was clogged of course.
The machine is dismanteled, descaled several times, backflushed and manually cleaned.
I also dismanteled the E61 grouphead and cleaned every part.
New group shower, new gasket, new pressurestat and new manometer for pressure.
The machine is now working, but there's no chance to get it to 9 bars.
With the original Ulka pump, it stopped at 5bars, and I tried two other identical pumps I had laying around (both from older machines), but still stopped at 6.5 bars.
Do I need a new 48W pump? There's nothing that indicates there's a problem elsewhere.

Any ideas?
Thanks in advance!!

I would focus on the OPV adjustment nd do so with a blind filter

I have tested many times now with blind filter. I also have a portafilter with bar manometer, same there, always stops at 6.5 bars.
There's nothing to adjust here besides the pressurestat. The OPV hiss a bit when heating up,but goes silent pretty fast. I can't see that there's anything wrong with it.

I descaled it again, and mixed in a small amount of Cafiza. Still some dirt in there, but not enough to stop it from hitting 9 bars.
All rubber tubes was removed and put in descaling bath, they are as new. No leaks from anywhere either.
My Rancilio Lucy has the same Ulca pump, and this has been running for almost 20 years, still hits 9 bars.
This is strange.

I squeezed the rubber tube (marked red) with my fingers, and the pressure went up, until it snapped of it's T-split. Could the rubber sealing on the E61 mushroom be the problem, letting tto much water back into the tank? (Replaced the gasket, but not with original part.)

I think you're saying that the pump isn't stalling. That the pump is fine but that all the brew-flow is going over the expansion valve when brew circuit pressure exceeds 5 bars. And I think you have proven it by squeezing the silicone tubing and briefly stopping the flow through the expansion valve. Can you not adjust the expansion valve that's letting the water into that tubing? If not, can you replace the expansion valve? (Replace it with an adjustable one, perhaps)?

Isomac OPV are adjustable,
assuming of course that you have the original one
take a photo and show it

subchannel wrote: The OPV hiss a bit when heating up,but goes silent pretty fast. I can't see that there's anything wrong with it.

No, that is the vacuum breaker, not the OPV

subchannel wrote: Could the rubber sealing on the E61 mushroom be the problem, letting tto much water back into the tank? (Replaced the gasket, but not with original part.)

No, but what you described is what happens when the overpressure valve/bypass valve is adjusted to low, has a weak spring, or has other contaminants in it preventing it from sealing.

Take the rubber return line out of the water reservoir. Put it in the glass. Pull a shot. If water pumps out of the line into the glass (some flow is normal) you have an issue with the OPV/bypass valve.

Thanks a lot for input guys! Problem solved. Not very easy to see the adjustment screw, but that was the issue.
I thought the OPV was the valve at the top of the boiler, next to the UPV?

Anyway, thanks a lot for good help!!

My friend is giving me his Wega Mininova EPU as payment for fixing his Isomac, so that will be the next project. 24 years old machine, not working/ leaking.