It looks that doing descaleing has blocked some out let's try removing by thing and run som worm water to remove or open channels if not you have to go inside to refix
leave the power point turned on.
turn off machine at the power switch (on the unit)
This should bring the unit down....or
Turn off completely unit and power point and the just turn on the power point...this should bring the unit down
Hi,I had the same problem with my Siemens EQ.300. The problem was residues that are sticked to brewing unit. Here is the solution for my Siemens EQ.300Take a plastic brush and clean all part of the brewing unit, deeply, under tap water for 5 minutes. Dry gently, and re-inserted to the Siemens EQ.300 machine.Update: After a while, same problem happened again. This time, I have washed my coffee machine's brewing unit in the dishwasher. Result is perfect!https://www.izreview.com/siemens-eq-3-espresso-coffee-machine-review/#Siemens_EQ300_dispensing_coffee_into_the_drip_tray
These machines are so complicated they have to serviced by authorized service centres at least once a year. Heat, pressure and plastic parts fail, plus neoprene O-Rings lose their lubrication properties and go hard. Yours needs dealer service.
Check the tank float, if it is not floating jam something plastic underneath it and then you will get rid of the error but will need to check water level yourself in future.