E21
Bosch Dryer
Severity: ModerateWhat Does This Error Mean?
E21 on a Bosch condenser dryer means the water container (condensation tray) or its float switch has a fault. The float switch detects when the water collection tray is full and triggers the dryer to stop. E21 appears when the switch reports the tray as full when it is not — or fails to report when it truly is full.
Affected Models
- Bosch WTH84000GB
- Bosch Serie 6 Condenser Dryer
- Bosch WTW876H0GB
- Bosch WTV74100GB
- Bosch condenser dryers with water collection tray
Common Causes
- Float switch stuck in the raised (full) position — causes the dryer to think the tray is always full
- Water tray not fully inserted — the tray must click fully into place for the switch to reset
- Float switch wiring loose or disconnected
- Tray damaged or deformed — no longer seating correctly against the float switch
- Condensate pump fault causing water to back up and keep the float raised
How to Fix It
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Pull out the water collection tray (top of the dryer on most models) and empty it completely.
Even if the tray does not look full, remove and empty it — sometimes a small amount of water sitting in the wrong position keeps the float switch raised.
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Rinse the empty tray and dry it, then slide it back in firmly until it clicks into place.
The tray must be fully inserted for the float switch to reset properly. Push it all the way in.
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Restart the dryer and run a short cycle.
If E21 clears and the cycle completes, the issue was the tray seating. Keep monitoring — if E21 returns quickly, the float switch is stuck.
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Inspect the float switch inside the tray compartment.
With the tray removed, look inside the compartment for a small plastic float switch mechanism. It should move freely up and down. If it is stuck in the raised position, carefully free it with a finger or soft brush.
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If E21 persists, call Bosch service — the float switch or its wiring needs professional attention.
A stuck or faulty float switch cannot be permanently fixed by manual adjustment — it needs to be replaced.
When to Call a Professional
If removing, emptying, and reinserting the tray does not clear E21, the float switch needs to be inspected. Float switch replacement is accessible on some models but requires disassembly on others — a technician can confirm. Contact Bosch service if the tray and basic checks do not resolve the fault.
Frequently Asked Questions
How often should I empty the Bosch dryer water tray?
Empty the water tray after every drying cycle — or at least every 1–2 cycles for small loads. A full tray stops the dryer mid-cycle. If you connect a drain hose at the back of the dryer, the tray fills much less often as water pumps directly to the drain.