Home Fault Codes

Noritz Tankless Water Heater Error Code 20: Meaning and Fix

Applies to: Noritz tankless water heaters (residential and Pro Series premix models; each Noritz help article notes which models it covers).

20
How 20 appears on a Noritz tankless water heater display.

Reading the tankless water heater display

A tankless water heater shows its fault as a number or letter code on the unit display or on the wired remote controller, and some models keep a short history of past codes. Write the code down exactly as shown before you reset the unit, and check the rating plate for the model number, because the same number can mean different things between series.

Noritz makes gas tankless water heaters that show a numeric error code on the display or the remote. Its help center documents each code, and the steps differ between residential and Pro Series premix models. Check the model label on your unit before using any chart.

What causes 20

How to fix it

If you smell gas, leave the building and call your gas utility from outside; do not touch switches or the unit. Switch the water heater off and let it cool before you touch any internal part, and call a licensed plumber or water heater technician if you are not sure.

The code meaning comes from the manufacturer document listed under Sources. The causes and steps below are general troubleshooting guidance, not the manufacturer's service procedure.

  1. Switch the water heater off and let it cool before you touch anything inside it. If you smell gas, leave the building and call your gas utility from outside.
  2. Start with a descale flush.
  3. Clean the combustion area if dust or lint is present.
  4. Do not keep resetting the unit without fixing the cause, because repeated trips can lead to code 14.
  5. If the code returns after these checks, call a licensed plumber or water heater technician and give them the code and the model number from the rating plate.

Questions

What does Noritz tankless error code 20 mean?

Code 20 on a Noritz Pro Series model means the high limit switch tripped, usually requiring a hard reset. The switch sits on the copper pipe leaving the heat exchanger.

Can I reset the water heater myself?

Turning the unit off and back on, or unplugging it for about 30 seconds, clears some codes. If the same code comes back, the fault is still there and the unit will shut down again. Do not bypass a safety device to keep it running.

When should I call a technician?

Call a licensed plumber or water heater technician for anything involving gas, venting, the heat exchanger, a thermal fuse or the circuit board, or when the code keeps returning after the simple checks.

Other Noritz tankless water heater codes

06Recirculation flow too low (NRCR)10Combustion warning (can lead to code 90)11Ignition failure12Flame loss14Heat exchanger overheat (thermal fuse)16Outlet water temperature too high

Sources

Part numbers are OEM references; confirm fit by your model number before ordering. Meanings compiled from manufacturer and parts-retailer documentation; see sources below. Unplug the appliance before opening it.