The F21 error on your Siemens Dishwasher means the appliance has detected a drainage problem, preventing water from being pumped out properly. This typically indicates a blocked drain pump, kinked hose, or faulty pump motor that needs attention.
| Error code | F21 |
|---|---|
| Meaning | Drainage fault - water not pumping out correctly |
| Severity | Medium — dishwasher cannot complete cycles until resolved |
| Time to fix | 15–45 minutes |
| Tools needed | Towels, bucket, screwdriver, pliers (optional) |
What the F21 error means
The F21 error code indicates your Siemens dishwasher cannot drain water properly. The control board has detected that water remains in the sump or tub after the drain pump has attempted to empty it. This drainage fault prevents the dishwasher from continuing its cycle and typically leaves standing water at the bottom of the machine. The error protects your dishwasher from potential flooding or damage to internal components.
Common causes
- Blocked or clogged drain pump filter containing food debris, broken glass, or small objects
- Kinked, twisted, or blocked drain hose preventing water flow to the sink or waste pipe
- Faulty drain pump motor that has failed or seized and cannot expel water
- Blockage in the household drain pipe or garbage disposal connected to the dishwasher
- Impeller inside the drain pump jammed by foreign objects like bones, labels, or bottle caps
- Faulty pressure sensor or switch giving incorrect readings to the control board
How to fix the F21 error
- Check and clean the drain filter: Turn off the dishwasher and remove the lower rack. Unscrew the filter assembly at the base of the tub and remove any debris, food particles, or foreign objects. Rinse thoroughly under running water and reinstall securely. This resolves the issue in approximately 60% of cases.
- Inspect the drain hose: Pull the dishwasher forward and check the drain hose for kinks, twists, or blockages. The hose should have a smooth upward loop before connecting to the sink drain or garbage disposal. Straighten any kinks and ensure the hose end is not pushed too far into the standpipe, which can cause an airlock.
- Check the garbage disposal and sink drain: If your dishwasher connects to a garbage disposal, ensure the knockout plug was removed during installation. Run the disposal to clear any blockages. Pour boiling water down the sink drain to clear grease or soap buildup that may be preventing proper drainage.
- Test the drain pump: Access the drain pump underneath the dishwasher (typically on the left side). Disconnect the hoses and check for blockages. Manually spin the impeller to ensure it rotates freely. If the pump motor is seized, makes unusual noises, or has visible damage, it needs replacement. A new Siemens drain pump costs approximately £40-80.
- Clean the sump area: Remove standing water with towels or a cup. Check the sump area beneath the filter for any objects, debris, or buildup that could obstruct water flow. Even small items like fruit stones or bottle caps can prevent proper drainage.
- Reset the dishwasher: After completing repairs, switch off the appliance at the mains for 5 minutes to reset the control board. Switch back on and run a rinse cycle to test if the F21 error has cleared. If the error persists after these steps, contact a qualified Siemens engineer as the pressure sensor or control board may require professional diagnosis.
FAQ
Can I still use my Siemens dishwasher with the F21 error showing?
No, you should not use the dishwasher when the F21 error appears. The appliance cannot drain properly, which means water will remain inside after cycles, potentially causing flooding, unpleasant odours, or damage to internal components. Resolve the drainage issue before running any cycles.
How much does it cost to fix a Siemens dishwasher F21 error?
If you resolve the issue yourself by cleaning filters and hoses, the cost is nothing beyond your time. If you need to replace the drain pump, expect to pay £40-80 for the part. Professional repair callouts typically cost £80-150 for labour plus parts. Most F21 errors are fixed by simple cleaning rather than part replacement.
Why does my Siemens dishwasher keep showing F21 even after cleaning?
If the F21 error returns after cleaning, the drain pump motor has likely failed and needs replacement. Alternatively, a faulty pressure switch may be sending incorrect signals to the control board, or there is a persistent blockage in your household plumbing beyond the dishwasher itself. Check that your sink drains freely and consider having your waste pipes inspected.
