Tumble Dryer
F20
The F20 error code on a Bosch tumble dryer signals a problem with the appliance’s moisture or humidity sensor system — specifically that the dryer cannot correctly detect how wet your laundry is. It’s a moderate fault: your dryer will stop working, but it’s often fixable at home without calling an engineer.
What does this error mean?
Bosch tumble dryers use moisture sensor bars inside the drum to measure how damp your clothes are, automatically adjusting the drying cycle length. When F20 appears, the machine is detecting an abnormal reading from these sensors — either no signal at all, a persistently wet reading, or a short circuit in the sensor circuit. In practical terms, the dryer cannot run an automatic cycle safely, so it shuts down to prevent over-drying or damage.
Est. repair cost
£15–£35 DIY (sensor bars or condenser clean); £80–£150 professional repair; up to £250 if control board replacement is needed
🔍 Likely causes
🛠️ Step-by-step fix
Reset the dryer first: turn it off at the wall, wait 5 minutes, then power it back on and start a new cycle. A temporary glitch can trigger F20 and a reset clears it.
Clean the moisture sensor bars: open the dryer door and locate the 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 in white vinegar or a mild descaler to remove fabric softener residue, then dry thoroughly.
Clean the lint filter and condenser unit: remove and rinse the lint filter under the tap, and — if you have a condenser dryer — pull out the condenser drawer at the bottom and rinse it with cold water until it runs clear. A blocked airflow system can cause false F20 readings.
Check the drum for visible damage to the sensor bars: if either metal strip is scratched through, broken, or heavily corroded, the sensor will need replacing. Replacement sensor bar kits for Bosch dryers cost approximately £15–£35 and clip in without tools — search your model number on a reputable UK parts supplier such as eSpares or 4ourhouse.
Inspect the wiring connector to the sensor bars: with the dryer unplugged from the mains, carefully check that the wire connector attached to the sensor is firmly seated and shows no signs of burning or corrosion. Re-seat it if loose. Do not open any sealed electrical panels — stop here and call a professional if the fault persists.
📞 When to call a professional
If cleaning the sensors and filters does not clear F20 after a full reset, or if you suspect a wiring fault beyond the visible connector, contact a Bosch-approved or Domestic & General engineer. Tell them: ‘My Bosch tumble dryer is showing error code F20, I’ve cleaned the moisture sensors and lint filter, and the fault persists — I need the sensor circuit and control board checked.’ Attempting to test or replace the control board yourself is not recommended as it involves working inside live electrical components.
⚖️ Repair or replace?
A professional repair for an F20 fault — typically sensor replacement or a wiring fix — will cost £80–£150 in the UK including labour. If the control board is at fault, expect £150–£250. For any Bosch tumble dryer over 8 years old where the repair exceeds £120, replacement is worth considering: a reliable new condenser dryer starts at around £350–£450. For a dryer under 6 years old in otherwise good condition, repair is almost always the better value.