Method of operating a heat pump laundry treatment apparatus, in particular a heat pump laundry dryer or a heat pump washing machine having drying function, wherein the laundry treatment apparatus comprises: a control unit controlling the operation of the laundry treatment apparatus and a control unit electronic board of the control unit, a laundry treatment chamber for treating laundry using process air, a process air circuit (20, 20a - 20d) for circulating the process air, a heat pump system having a refrigerant loop in which the refrigerant fluid is circulated through a first and a second heat exchanger (10, 12), a compressor for circulating the refrigerant fluid through the refrigerant loop and having a compressor motor, and a cooling fan unit for cooling the compressor, wherein during the operation the conveyance capacity of the cooling fan unit is varied, characterized by a motor electronic board being at least one of the following motor electronic boards: a motor electronic board for supplying controlled power to a drum motor for rotating a drum being the laundry treatment chamber, a motor electronic board for supplying controlled power to a process air fan motor for circulating the process air in the process air circuit, and a motor electronic board for supplying controlled power to the compressor motor; a detector unit configured for detecting an operation parameter indicating a state of the motor electronic board, wherein the motor electronic board operation parameter is at least a motor electronic board temperature (T_inv), and indicative of a current delivered by the motor electronic board to the motor exceeding a threshold value or exceeding a threshold averaged value; and wherein the method comprises: operating the cooling fan unit in dependency of the motor electronic board operation temperature (T_inv), and/or controlling the compressor operation output (OUT_comp, RPM_comp) in dependency of the motor electronic board operation temperature (T_inv), wherein the compressor motor is a variable speed compressor motor. a control unit controlling the operation of the laundry treatment apparatus and a control unit electronic board of the control unit, a laundry treatment chamber for treating laundry using process air, a process air circuit (20, 20a - 20d) for circulating the process air, a heat pump system having a refrigerant loop in which the refrigerant fluid is circulated through a first and a second heat exchanger (10, 12), a compressor for circulating the refrigerant fluid through the refrigerant loop and having a compressor motor, and a cooling fan unit for cooling the compressor, wherein during the operation the conveyance capacity of the cooling fan unit is varied, characterized by a motor electronic board being at least one of the following motor electronic boards: a motor electronic board for supplying controlled power to a drum motor for rotating a drum being the laundry treatment chamber, a motor electronic board for supplying controlled power to a process air fan motor for circulating the process air in the process air circuit, and a motor electronic board for supplying controlled power to a drum motor for rotating a drum being the laundry treatment chamber, a motor electronic board for supplying controlled power to a process air fan motor for circulating the process air in the process air circuit, and a motor electronic board for supplying controlled power to the compressor motor; a detector unit configured for detecting an operation parameter indicating a state of the motor electronic board, wherein the motor electronic board operation parameter is at least a motor electronic board temperature (T_inv), and indicative of a current delivered by the motor electronic board to the motor exceeding a threshold value or exceeding a threshold averaged value; and wherein the method comprises: operating the cooling fan unit in dependency of the motor electronic board operation temperature (T_inv), and/or controlling the compressor operation output (OUT_comp, RPM_comp) in dependency of the motor electronic board operation temperature (T_inv), wherein the compressor motor is a variable speed compressor motor. operating the cooling fan unit in dependency of the motor electronic board operation temperature (T_inv), and/or controlling the compressor operation output (OUT_comp, RPM_comp) in dependency of the motor electronic board operation temperature (T_inv), wherein the compressor motor is a variable speed compressor motor.