fa fault or 11 flashes Optical water indicator, use a tooth brush and clean the black grid thing that sits in the sump, if its really bad you can twist it out and clean it that way.
Had one of these yesterday.
Ended up being a write off, as the circ pump rubber hose had been leaking :rolls: and been spraying over the heater for a while causing it to short to earth.
Motor, heater and a possible board fault as it was also giving F1 code intermittently 🙁 .
Usually a toothbrush job though 😉
TC