Ariston Oven Error Code ER21

ER21 means the NTC temperature sensor on the power supply board is producing readings that the oven's control system considers illogical. The NTC is a resistive sensor used to monitor the thermal state of the power supply board electronics. When the control system cannot reconcile the sensor data with expected values, it triggers ER21 and may prevent the oven from operating to protect the electronics.

Cycling power to the oven may temporarily clear the ER21 display, but if the underlying cause is a failed NTC sensor or faulty power supply board, the error will return once the oven operates again. A reset does not repair the hardware fault. Persistent reappearance of ER21 after a power cycle confirms that component-level diagnosis and repair are needed.

Repair costs for ER21 vary depending on the specific oven model and local labor rates. The power supply board itself typically falls in the range of $80 to $200 for the part, with additional labor costs bringing the total repair estimate to roughly $150 to $350. Getting a quote from a qualified technician after diagnosis is recommended, as costs can vary significantly by region.

The primary fix for ER21 is replacement of the power supply board, which involves working inside the oven's electrical enclosure. Before replacing the board, a technician should check that all wiring connectors between the power supply board and the main control board are secure and free of corrosion. This repair requires disconnecting mains power and working with internal components, so it is best performed by a qualified appliance technician.

It is not advisable to continue using the oven while ER21 is active. The NTC on the power supply board monitors the thermal condition of the board's electronics, and if that protection is compromised, there is a risk of undetected overheating within the control electronics. Discontinue use until the fault has been diagnosed and repaired.