Tumble Dryer
F20
The F20 error code on a Siemens tumble dryer signals a moisture sensor or humidity detection fault — it’s a moderately serious issue that will stop your machine drying clothes properly, but it’s often something you can resolve yourself without calling an engineer.
What does this error mean?
The F20 code tells you that the dryer’s moisture (humidity) sensors are not reading correctly — either they’ve stopped detecting moisture in the drum, or they’re getting a signal that’s outside the expected range. Siemens tumble dryers use these sensors to decide when your laundry is dry and to regulate the drying cycle automatically. When the sensors fail or are obstructed, the machine throws F20 and may cut the cycle short or refuse to start.
Est. repair cost
£80–£150 professional repair; £10–£30 DIY moisture sensor part if self-replacing
🔍 Likely causes
🛠️ Step-by-step fix
Reset the machine first: unplug the dryer from the mains, wait 5 minutes, then plug back in and restart the cycle. A one-off electronics glitch can trigger F20 and a hard reset clears it.
Clean the moisture sensor bars: open the dryer door and look for two small metal strips on the inside of the drum (usually near the front, below the door seal). Wipe them firmly with a cloth dampened with white vinegar or rubbing alcohol to remove fabric softener residue and limescale. Dry thoroughly before use.
Clean the lint filter: remove the filter (usually in the door aperture or on top of the machine), pull off all lint by hand, then rinse under a tap and leave to dry fully before replacing. Do this after every single cycle going forward.
Clean the condenser unit (condenser or heat pump models only): locate the condenser behind the kick plate at the bottom front of the machine. Remove it, rinse it under a cold tap until the water runs clear, and leave it to dry completely before refitting. Refer to your model’s manual for exact removal steps.
Check for visible wiring damage: if the steps above don’t clear the fault, pull the dryer away from the wall and inspect the back panel for any visibly pinched, burnt, or disconnected wiring. Do not open the machine’s internal panels — if you suspect a loose internal connector or PCB fault, stop here and call a professional.
If F20 persists after all of the above, the moisture sensor itself likely needs replacing. Genuine Siemens sensor strips for common models are available from UK appliance parts suppliers (e.g. eSpares, 4ourhouse) and can be swapped without opening electrical components on most models — search your full model number to confirm compatibility.
📞 When to call a professional
Call a qualified appliance engineer if the F20 error returns after cleaning the sensors and filters, if you suspect a wiring or control board fault, or if your machine is showing additional error codes alongside F20. When you call, tell the engineer: ‘My Siemens tumble dryer is showing error code F20 — I’ve cleaned the moisture sensors and filters but the fault persists, so I think it may be a sensor, wiring, or PCB issue.’ This will save diagnostic time and money.
⚖️ Repair or replace?
A professional repair for an F20 fault — typically a sensor replacement or wiring fix — costs around £80–£150 in the UK including parts and labour. If your Siemens dryer is under 5 years old, repair is almost always the right call. If it’s over 8–10 years old and repair costs exceed half the price of a new equivalent model (budget £400–£700 for a comparable Siemens), replacement makes more financial sense.