F21Serious
Bosch Dryer F21 Error Code
The heater relay is stuck in the closed position, causing continuous heating even when dryer should be cooling down.
Common causes
- Faulty relay on control board
- Control board damage
- Moisture or corrosion on board
How to fix it
- Unplug dryer and inspect control board for burn marks.
- Check for sticky relay (listen for click when power on).
- If relay is stuck, do not operate dryer; risk of fire.
⚠ When to call a pro: Immediately call a technician; control board replacement is required.
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Always unplug the appliance (and turn off the water for washers/dishwashers) before inspecting. These guides are for information only and are not a substitute for a professional repair.