Bosch Refrigerator Error Code F15

The F15 error code on a Bosch refrigerator indicates that the automatic defrost cycle in the freezer compartment has failed on two consecutive attempts. During a normal defrost cycle, the control board activates a defrost heater to melt frost accumulation from the evaporator coils. The system monitors evaporator temperature via the evaporator sensor, and a successful cycle requires that temperature to rise above -12°C. When the sensor reports that this threshold was not reached after two back-to-back defrost attempts, the board logs F15 and typically suspends further defrost attempts to prevent potential damage.

The defrost circuit includes three primary components that are each capable of causing this failure: the defrost heater itself, the safety thermal cut-out (also called a thermal limiter or high-limit thermostat), and the evaporator temperature sensor. The heater is a resistive element that generates heat when current passes through it. The thermal cut-out is a one-time or resettable safety device wired in series with the heater that opens the circuit if the evaporator reaches an unsafe temperature. If either the heater is open-circuit or the thermal cut-out has blown, no heat is produced regardless of whether the control board sends the correct actuation signal.

A failed evaporator sensor adds a diagnostic complication: even if the heater is functioning correctly and melting frost, an out-of-range or stuck sensor reading can falsely report that -12°C was never reached, triggering F15 without any actual heating problem. Wiring faults between the control board and these components, including loose connectors or chafed insulation, can also interrupt the circuit intermittently and cause the same failure pattern.