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How do you fix a Noritz error code 51?

Alton Alexander
By Alton AlexanderUpdated on June 4th, 2022

The Noritz Error Code 51 is a tankless water heater error code that indicates a problem with the water temperature sensor. This error code can happen for a variety of reasons, including a faulty or damaged sensor, a loose connection, or a problem with the wiring. If you see this error code, it's important to call a qualified technician to diagnose and repair the problem.

Other common searches for this error include:

  • noritz error code 903
  • noritz error code 20
  • noritz error code 67
  • noritz error code 51

1. Restart the water heater

  1. Open the water heater access panel.
  2. Remove the screws that hold the water heater in place.
  3. Lift the water heater off of the mounting bracket.
  4. Replace the water heater mounting bracket and screws.
  5. Reconnect the water heater to the power supply.
  6. Turn on the water heater.
  7. Check the water heater for leaks.
  8. If there are no leaks, reset the water heater error code to 0.

2. Check the power supply to the water heater

  1. Verify that the power supply to the water heater is working. If the power supply is not working, then the noritz error code 51 will appear.
  2. Check the power cord to the water heater to make sure that it is properly plugged into an outlet.
  3. Check the fuse box to make sure that the fuse for the water heater is intact and properly working.
  4. Check the breaker panel to make sure that the breaker for the water heater is intact and properly working.
  5. Check the power supply to the water heater to make sure that the power is coming from the correct source. If the power is coming from an erroneous source, then the noritz error code 51 will appear.

3. Check the thermostat settings

  1. Open the car's door and locate the thermostat.
  2. Press and hold the "H" button on the key fob until the car's display shows "THERMOSTAT".
  3. Look for the "Temp" tab on the display and press the "SET" button.
  4. Use the up and down arrows to select "C" and press the "SET" button.
  5. Look for the "Temp" setting and press the "SET" button.
  6. Use the up and down arrows to select the desired temperature and press the "SET" button.
  7. Press the "END" button to exit the thermostat settings.
  8. If the error code disappears, the thermostat may have been replaced and should be replaced. If the error code remains, the thermostat may need to be replaced.

4. Check for blockages in the water heater

  1. Turn off the water heater at the main supply and check for any obstructions in the water line.
  2. If there are no obstructions, turn on the water heater at the main supply and wait a minute for it to come up to temperature.
  3. Look for any areas on the water heater where the water is not circulating freely.
  4. If there are any areas where the water is not circulating freely, use a plunger to clear any obstructions.
  5. Turn off the water heater at the main supply and check for any obstructions in the water line.
  6. If there are no obstructions, turn on the water heater at the main supply and wait a minute for it to come up to temperature.
  7. Check for any areas on the water heater where the water is not circulating freely.
  8. If there are any areas where the water is not circulating freely, use a plunger to clear any obstructions.
  9. If the water heater still does not work, contact a professional.

Still not working? maybe try one of these options:

  1. Check the gas supply to the water heater.
  2. Check for leaks in the water heater.
  3. Replace the thermostat.
  4. Replace the gas valve.
  5. Replace the water heater.