KitchenAid Cooktop Error Code U400

The U400 code means the cooktop's internal voltage monitoring circuit has detected that the appliance is connected to a 400V supply instead of the correct lower voltage. The warning activates when measured grid voltage reaches approximately 280 volts, and has been observed triggering at voltages as low as 250 volts. This is a supply voltage error, not an internal component failure. The cooktop is protecting itself from damage caused by the incorrect connection.

No, you should not continue operating the cooktop while U400 is active. The code indicates the appliance is receiving voltage outside its rated parameters, which can damage the power control electronics, induction drive components, and other internal circuitry. Disconnect the unit from the power supply and do not reconnect it until the supply voltage has been verified and corrected by a qualified electrician.

Because U400 is a supply voltage issue rather than a parts failure, the primary cost is typically an electrician service call to diagnose and correct the wiring, which generally ranges from $100 to $300 depending on the complexity of the fix and local labor rates. If a transformer needs to be replaced or panel work is required, costs can range higher, from $200 to $600 or more. If the cooktop was operated under incorrect voltage for an extended period and internal components were damaged, board or inverter replacement could add $150 to $500 in parts and labor.

Start by disconnecting the cooktop from the AC line immediately to prevent potential damage. Have a licensed electrician measure the voltage at the cooktop's supply terminals and trace the wiring back to confirm the correct voltage is being supplied. Once the supply voltage is corrected to the proper rated level, the U400 error will clear without any additional steps needed inside the cooktop.

A simple reset will not permanently clear U400 because the error is caused by an external supply voltage condition, not an internal fault that resets. If the incorrect voltage is still present at the terminals, the code will return as soon as the cooktop is powered back on. The error will only clear and stay clear once the underlying voltage supply issue has been corrected.