Miele G1220 F14 appears 2min into any wash cycle?

Hi all helpers!
I have done extensive research on this Error F14 and tried a couple of things but can't get it fixed. Let me describe the problem:
I cleaned the machine (sieve, non-return valve, spray arms etc) as it hasn't been cleaned in a while.
When I removed the non-return valve to clean, the sealing o-ring was brittle and falling into pieces and consequently didn't seal anymore. So I ordered a new one.

After that, the machine has worked fine two or three times. But then it started having error F14 about 2 min into the cycle. Now, when I try 10-15 times I might get lucky and it runs all the way through just once.
This is what happens in any program:
It pumps water in.
Hums.
Fills with water to about 1cm below the sieve handle.
Hums.
The middle spray arm turns and sprays water for 4 revolutions.
It stops.
Machine gurgles a bit.
Then hums again.
Water stays in the bottom. M
iddle spray arm turns 4 times etc. as above.
This procedure happens about 6 times in total.
Then the Bottom arm does one revolution.
Then F14 appears.
Then the water gets pumped out.

Have disconnected and reconnected from power and water supply. Checked for kinks or blockage in inlet hose.
Added water at beginning of the cycle. No luck...

Any idea how to narrow down the problem and fix it? Read all posts here about circulation pump, heater switch, etc... Just don't want to fiddle around with every single part ...maybe someone knows what exactly it could be?