What it means
Shown as E1 then 21 (or C1 then 21) on two-digit displays. Samsung lists the indoor heat exchanger sensor separately as E122 / C122. On Samsung EHS heat pumps, the control kit manual lists E121 as a short or open circuit in the Zone 1 room temperature sensor.
What to check, in order
- Reset the power once
Samsung's service pages suggest unplugging the indoor unit for about 10 seconds, or switching it off at the breaker if it has no plug, then turning it back on.
- Write the code down
Samsung's support pages say this fault needs an authorised service centre, so note the code before you call.
When to call an engineer
Book an engineer if the code returns. Samsung's support pages say the room temperature sensor (thermistor) is shorted or defective, and its Smart Install guide has the engineer check that the sensor is properly connected.
A repair visit will usually check the sensor's reading and its wiring.
- Note the model and serial number. They're on a label on the side of the indoor unit, and on the outdoor unit.
- Write down the exact code, and what the appliance was doing when it appeared.
- Check whether it's still under warranty. If it is, the repair may cost you nothing.
Quick answers
What does the Samsung E121 error code mean?
The sensor that reads the room temperature in the indoor unit is not working properly. Samsung says the unit may not turn on while this sensor is shorted or defective. Shown as E1 then 21 (or C1 then 21) on two-digit displays. Samsung lists the indoor heat exchanger sensor separately as E122 / C122. On Samsung EHS heat pumps, the control kit manual lists E121 as a short or open circuit in the Zone 1 room temperature sensor.
Can I fix Samsung E121 myself?
Engineer only (engineer visit). Start with: reset the power once; write the code down. Book an engineer if the code returns. Samsung's support pages say the room temperature sensor (thermistor) is shorted or defective, and its Smart Install guide has the engineer check that the sensor is properly connected.
Is Samsung E121 worth repairing?
Worth fixing. A sensor or its connection is a small repair and normally worth doing.
Checked against
- Samsung Gulf support: Error codes on Samsung indoor air conditioner
- Samsung Philippines support: Check out the displayed error codes on the indoor unit air conditioner
- Samsung Electronics Service (Korea): air conditioner inspection codes 100 to 199 (Korean)
- Samsung India support: Samsung AC Smart Install guide (error codes for installers)
- Samsung AR10RYFT / AR13RYFT wall-mounted air conditioner service manual (PDF), 'Display Error and Check Method' (copy on notice-facile.com)
Last reviewed October 2026. Manufacturers update their pages, and your manual is the final word. Spotted a mistake? Email contact@appliance-error-codes.com.