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Error code reference

Bosch Dryer Error Code 4

Overheating

Bosch codesBosch dryer codes

Overheating – Extra dry LED flashes in the progress indicator, indicating an overheating condition. If temperature does not drop below limit within 10x30 sec, drying is terminated.

First step from the service manual

Clean the fluff filter; check air-intake/exhaust-air passages for blockages.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What 4 means on a Bosch dryer

Error code 4 on a Bosch dryer signals an overheating condition within the drum or airflow system. When this fault is active, the Extra Dry LED flashes in the progress indicator to alert the user. The dryer's control system monitors internal temperature continuously, and if the temperature fails to drop below the defined safety threshold within 10 consecutive 30-second intervals (a total of 5 minutes), the drying cycle is automatically terminated to prevent damage to the appliance or laundry.

The overheating condition is almost always linked to restricted airflow. When the dryer cannot move air efficiently through the system, heat builds up inside the drum faster than it can be expelled. The fluff filter, exhaust duct, and air-intake passages are the primary points where blockages develop. A heavily clogged lint filter alone can drastically reduce airflow volume, forcing the heating element to cycle at elevated temperatures with inadequate cooling.

In some cases, the fault may persist even after airflow restrictions are cleared, pointing to a faulty thermostat, thermistor, or temperature limiter that is not accurately reporting or regulating drum temperature. A failed exhaust fan motor can also produce this code by reducing airflow even when ducts and filters are clear. Diagnosing the root cause requires systematically ruling out blockages before moving to component-level testing.

Source: manufacturer service documentation.

Common causes of 4

  1. 01

    Clogged fluff filter

    Wiring / connection

    A lint-packed filter blocks airflow through the drum, trapping heat and triggering the overheat fault. Remove and clean the filter thoroughly before every cycle, and inspect it as the first step when error code 4 appears.

  2. 02

    Blocked or kinked exhaust duct

    Wiring / connection

    Lint buildup, kinks, or crushing in the exhaust hose restricts hot air from leaving the dryer. Inspect the full length of the duct run, check the exterior vent flap for blockage, and clear any obstructions found.

  3. 03

    Restricted air-intake passages

    Wiring / connection

    The dryer requires unrestricted intake air to cool its components and support airflow through the drum. Blockages at intake grilles, or positioning the dryer too close to a wall, can reduce incoming airflow and contribute to overheating.

  4. 04

    Faulty thermostat or temperature limiter

    Part replacement

    If airflow paths are clear and overheating still occurs, the thermal limiter or thermostat may be failing to regulate or accurately sense drum temperature. These components require testing with a multimeter and replacement if found to be out of specification.

  5. 05

    Failed exhaust fan motor

    Part replacement

    A worn or seized exhaust fan motor cannot move adequate air volume through the system even when ducts are unobstructed. Listen for reduced fan noise during operation and inspect the motor if airflow at the external vent feels weak.

See the test procedure for each cause

Frequently asked questions about 4

What does 4 mean on a Bosch dryer?
Error code 4 on a Bosch dryer indicates an overheating condition. The Extra Dry LED flashes in the progress indicator while the dryer monitors whether the temperature drops below the safety limit. If the temperature does not come down within 10 intervals of 30 seconds each, the dryer automatically stops the cycle to prevent damage.
How do I fix error code 4 on my Bosch dryer?
Start by removing and thoroughly cleaning the fluff filter, then inspect the exhaust duct and air-intake passages for any blockages or kinks. Make sure the exterior vent flap is opening freely and that the dryer has adequate clearance for intake air. If the error returns after clearing all airflow restrictions, a component such as a thermostat, temperature limiter, or exhaust fan motor may need to be tested and replaced.
Is it safe to keep using my Bosch dryer when error code 4 appears?
No, you should not continue running the dryer while the overheating fault is active. The dryer automatically terminates the cycle as a safety measure, and bypassing or repeatedly resetting without resolving the root cause risks damage to the appliance and could pose a fire hazard. Resolve the underlying airflow restriction or component fault before resuming use.
Will resetting my Bosch dryer clear error code 4?
A reset may clear the displayed fault and allow the dryer to restart, but the error code 4 will return if the underlying cause has not been addressed. The overheating condition is tied to actual temperature readings inside the machine, so fixing the airflow restriction or faulty component is necessary for a lasting resolution.
How much does it cost to repair a Bosch dryer showing error code 4?
If the fix is simply cleaning the lint filter and clearing a blocked duct, there is no parts cost involved. If a component like a thermostat, temperature limiter, or exhaust fan motor needs replacement, parts and labor together typically range from around $100 to $300 or more depending on the specific component and your location. Getting a diagnostic inspection from a qualified technician can help confirm which parts are actually needed before committing to repairs.

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