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Error code reference

A.O. Smith Water Heater Error Code 13

Temperature sensor (thermistor) inside the immersion probe is open.

A.O. Smith codesA.O. Smith water heater codes
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What the 13 error code actually means

Your water heater's built-in temperature sensor has stopped sending a readable signal to the control board, so the heater has shut down as a safety precaution. This usually means the sensor itself has failed or there is a wiring problem between the sensor and the control board. Turning the unit off for about 15 seconds and back on is the first thing to try, but if the error comes right back, a technician will need to inspect and likely replace the sensor.

Diagnostic procedure

The full 13 procedure

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First diagnostic step
Turn power off for 10 to 20 seconds then on again to clear the error code.
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Most common causes of 13

Ranked by how often they cause this code
  1. 1Failed thermistor inside the immersion probe
  2. 2Loose or corroded connector at the probe
  3. 3Damaged wiring in the sensor harness
  4. 4Corrosion or scale buildup on the probe
  5. 5Transient electrical fault or power surge

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Questions people ask about 13

What does 13 mean on a A.O. Smith water_heater?
Error code 13 means the temperature sensor (thermistor) inside the immersion probe is registering as an open circuit. The control board cannot receive a valid temperature reading, so the unit shuts down to prevent unsafe operation. This fault points to a failed thermistor, a wiring issue, or a faulty connection between the probe and the control board.
How do I fix error code 13 on an A.O. Smith water heater?
Start by cycling the power off for 10 to 20 seconds to clear the fault. If the code returns, inspect the immersion probe connector and wiring harness for loose connections, corrosion, or visible damage. Use a multimeter to check resistance across the thermistor leads: an open reading (infinite resistance) confirms the probe needs replacement. If wiring and connectors check out, replacing the immersion probe assembly is the appropriate repair.
How much does it cost to repair error code 13 on an A.O. Smith water heater?
Repair costs depend on the root cause. If only a connector needs cleaning or reseating, the labor cost may be minimal, typically in the range of $50 to $150 for a service call. If the immersion probe assembly requires replacement, parts and labor combined generally fall in the range of $100 to $350, depending on the specific model and local labor rates. A full wiring harness replacement would be at the higher end of that range.
Will resetting the water heater clear error code 13?
Turning the power off for 10 to 20 seconds and then back on will clear the stored fault code and allow the unit to recheck the sensor. If the error code does not return after the reset, the fault was likely a transient electrical issue. If code 13 comes back immediately or shortly after the reset, the underlying problem with the thermistor or its wiring is still present and requires further diagnosis.
Is it safe to use my water heater when error code 13 is displayed?
When code 13 is active, the water heater will typically shut down and not heat water, which is a protective response to the loss of temperature monitoring. Operating a water heater without a functioning temperature sensor creates a risk of uncontrolled heating or overheating. It is best to keep the unit off until the fault is diagnosed and repaired.

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