E18/F18 on Siemens is related to a blocked filter or drain hose. Cleaning depends on the access described in your E-Nr. manual.
Check the outlet and wastewater
The E18/F18 code appears in the manufacturer documentation. Check the hose without moving the appliance abruptly: a crushed bend or a blocked siphon can prevent draining. If the installation is recent, compare the height and connection with its diagram.
Drain before cleaning
Turn it off and disconnect it safely, let the water cool, and prepare a container. Use the drain tube or the gradual filter opening described in the manual. Do not remove the plug completely while water is still waiting to drain.
Once empty, clean any accessible residue and refit the filter with its seat clean and closed. Check any connections you touched to avoid the drain clearing leaving a leak. Consult pump filter maintenance if you need to prepare for that task.
If there is no user access or the code returns with the path clear, seek assistance. Hearing a pump run does not prove it has enough flow, and the error does not by itself mean it needs to be replaced.
Note whether the water drains normally after cleaning or whether the same level remains trapped.