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Error code reference

Bosch Dryer Error Code 1

NTC R4 fault

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NTC R4 fault – the 'Drying' LED flashes in the progress indicator, indicating an NTC thermistor fault for the sensor located in the air current in front of the heater.

First step from the service manual

Check if appliance ambient temperature is below 0°C; if so, instruct customer not to operate below 0°C. Otherwise, remove cable from power module and test NTC R4, cable, and plug-and-socket connection.

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

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What 1 means on a Bosch dryer

Error code 1 on a Bosch dryer indicates a fault with NTC thermistor R4, which is the temperature sensor positioned in the air current directly in front of the heater. NTC (Negative Temperature Coefficient) thermistors change their electrical resistance in response to temperature: as temperature rises, resistance falls. The dryer's control module continuously monitors the resistance reading from R4 to track air temperature entering the heater assembly. When the module detects a reading outside the expected range, either an open circuit, a short, or an implausible value, it triggers this fault and signals the problem by flashing the 'Drying' LED in the progress indicator.

The fault can originate in three distinct locations: the thermistor itself, the wiring harness connecting it to the power module, or the plug-and-socket connection at either end of that cable. Before condemning any component, the ambient temperature of the installation space must be checked. NTC sensors produce resistance values that shift dramatically at low temperatures, and operating the appliance below 0°C will cause the control module to read the sensor as faulty even when all hardware is functioning correctly.

Diagnosis begins by disconnecting the cable from the power module and testing R4's resistance directly, then inspecting the cable for continuity and the connectors for corrosion, bent pins, or loose seating. A failed thermistor, damaged harness, or compromised connector will each produce an out-of-range signal that prevents safe heater operation, which is why the dryer halts and displays this code rather than continuing to run.

Source: manufacturer service documentation.

Common causes of 1

  1. 01

    Faulty NTC R4 thermistor

    Part replacement

    The thermistor itself may have failed internally, producing a resistance value outside the acceptable range or showing an open circuit. Testing the component directly after disconnecting the cable from the power module will confirm whether resistance is within the expected range for the current ambient temperature.

  2. 02

    Damaged or broken wiring harness

    Part replacement

    The cable running between the NTC R4 sensor and the power module can develop breaks, shorts, or chafing due to heat exposure or vibration over time. A continuity test on the cable with it disconnected at both ends will identify any open or shorted conductors.

  3. 03

    Loose or corroded plug-and-socket connection

    Wiring / connection

    The connector joining the sensor cable to the power module can work loose, corrode, or develop bent pins, causing an intermittent or absent signal. Inspect both the plug and socket for discoloration, corrosion buildup, or pins that are not fully seated.

  4. 04

    Installation ambient temperature below 0°C

    Wiring / connection

    If the dryer is installed in an unheated garage, basement, or utility space that drops below freezing, the NTC sensor will produce a resistance reading the control module interprets as a fault. No parts are needed; the appliance should simply not be operated in sub-zero conditions.

See the test procedure for each cause

Frequently asked questions about 1

What does 1 mean on a Bosch dryer?
Error code 1 on a Bosch dryer signals a fault with the NTC R4 thermistor, the temperature sensor located in the air current in front of the heater. The dryer uses this sensor to monitor incoming air temperature, and when the reading falls outside the expected range, the control module shuts down and flashes the 'Drying' LED to alert you. The fault can be caused by a failed sensor, a wiring problem, a bad connector, or an installation environment that is below 0°C.
Can I fix error code 1 on my Bosch dryer myself?
If the dryer is installed somewhere that gets below 0°C, the fix is simply moving it to a warmer location or waiting until temperatures rise. Beyond that, resolving this code requires disconnecting the sensor cable from the power module and testing the thermistor, cable, and connectors with a multimeter, which is a task suited to someone comfortable with basic electrical testing. If the thermistor or harness is confirmed faulty, replacing those components will require some disassembly of the dryer cabinet.
Is it safe to keep using my Bosch dryer when error code 1 appears?
No, you should not continue operating the dryer while this error is active. The NTC R4 sensor provides the control module with temperature data used to manage the heater safely, and running the appliance without a reliable reading from that sensor creates a risk of overheating. The dryer's built-in protection has already halted operation for this reason, and normal use should not resume until the fault is diagnosed and corrected.
Will resetting my Bosch dryer clear error code 1?
A power reset may temporarily clear the displayed fault, but the underlying problem with the NTC R4 thermistor, its wiring, or its connector will remain. If the sensor continues to produce an out-of-range signal, the error code will return as soon as the dryer attempts to run a cycle. Proper diagnosis and repair of the faulty component is required for a lasting fix.
How much does it cost to repair error code 1 on a Bosch dryer?
If the fix is simply reseating a loose connector or moving the appliance out of a freezing environment, there may be little to no cost involved. Replacing the NTC R4 thermistor is a relatively affordable repair, with parts and labor typically ranging from around $75 to $200 depending on your location and service provider. If the wiring harness also needs replacement, costs can rise toward the higher end of that range or beyond.

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