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Samsung Air Conditioner E121 Error Code

Room temperature sensor fault. Here is what it means and how to clear it, easiest fix first.

E121
May need a pro

The sensor that reads room air temperature at the indoor unit has an open or short circuit, or isn't connected properly. Samsung says that when this alarm shows and the unit refuses to turn on, a shorted or failed room sensor is the likely cause.

Samsung uses an E or a C as the first letter depending on model year, so E121 and C121 are the same fault. Wall-mount units with a small two-digit display may show the code in two parts, such as E1 (or C1) followed by 21. These meanings come from Samsung's support pages for markets outside the US (such as the UAE, India, Malaysia and the Philippines); codes and display formats vary by model and region, so check your owner's manual.

Safety first: unplug the air conditioner (or switch off its breaker) before touching filters, hoses or panels. If you smell burning or gas, or see water near the outlet, stop and call a professional.

How to fix Samsung E121

  1. Reset the power at the breaker

    Switch off the breaker that feeds the air conditioner (some systems have separate breakers for the indoor and outdoor units, so switch off both). Wait about five minutes, switch the power back on and restart the unit to see if the code clears.

  2. Note the full code and model number

    If the code returns, write down exactly what the display shows, including both parts of a two-part code such as E1 then 21, and the model number from the label on the side of the indoor unit. Sensor and board parts differ between models, so this lets the technician bring the right part on the first visit.

When to call a technician

A sensor fault needs a technician to test and replace the thermistor. Samsung lists this as a code for an authorized service center.

Parts that commonly cause E121

Order parts by your exact model number so they fit.

Other Samsung air conditioner codes

Frequently asked questions

What does E121 mean on a Samsung air conditioner?

The sensor that reads room air temperature at the indoor unit has an open or short circuit, or isn't connected properly. Samsung says that when this alarm shows and the unit refuses to turn on, a shorted or failed room sensor is the likely cause.

Can I fix Samsung E121 myself?

Only the basic checks. You can safely try the steps above, but E121 usually points to a part or fault that needs a technician.

What if E121 keeps coming back?

A code that returns after a reset and the checks above usually means a part is wearing out. Note when E121 appears (which cycle, how often) and have your model number ready; it helps a technician bring the right part on the first visit.

Last reviewed 2026-10-19. Codes and steps can vary by model; check your owner's manual.

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