An F05 would suggest, a waste pipe or pump failure.
Please check for blockages in your pump filter (if applicable to model – please see user handbook). Also check for any blockages in waste water hose and in any under-sink plumbing. If none of the above solutions work, it is likely you have a pump failure and will need and engineer call out.
The majority of cases it will be due to a blocked filter, please let me know how you get on.