USA Expert Plumbing

Noritz tankless water heater maintenance: a yearly checklist

By USA Expert Plumbing Editorial Team. Updated . 2 min read.

Short answer

Noritz tankless heaters need a yearly checkup: flush the heat exchanger to remove scale, clean the water filter, check the air supply and exhaust venting, the relief valve and water connections, and on condensing models the condensate drain and neutralizer. Codes such as C1, 20, 92 and 93 warn you when service is overdue.

In this guide
  1. Yearly checklist
  2. Codes that point to maintenance
  3. How to flush a Noritz
  4. After long periods without use
  5. Winter

Noritz is direct about what skipping maintenance costs. Its knowledge base names scale buildup as the most common cause of both error code 20 and error code 14, and a code 14 usually means replacing the heat exchanger.

Yearly checklist

TaskWhy
Flush (descale) the heat exchangerPrevents overheating codes and heat exchanger damage
Clean the water filterA clogged filter slowly reduces hot water output
Check the air supply and exhaust ventsDust, soot or blockage cause combustion codes
Check the relief valve and water connectionsCatches leaks and pressure problems early
Check the condensate drain (condensing models)A blocked drain causes shutdowns
Check the neutralizer (condensing models)Built-in neutralizers wear out and must be replaced
Keep the area clearNo laundry, paper, sprays or other combustibles near the unit

Codes that point to maintenance

  • C1 (premix models): a scale buildup warning. Flush the heat exchanger.
  • 20: the high limit switch tripped, most often because of scale. Noritz warns that repeated code 20s can end in a code 14.
  • 14: the thermal fuse blew after a severe overheat. It cannot be reset.
  • 92 and 93: the built-in condensate neutralizer is near or at the end of its life.
  • 10: a combustion warning often linked to venting or air flow.

How to flush a Noritz

Most installations include isolation valves with service ports for flushing. The general sequence is:

  1. Turn off the heater at its controller, disconnect power and close the gas supply valve.
  2. Close the hot and cold isolation valves under the unit.
  3. Connect a small submersible pump and hoses to the service ports, with the pump sitting in a bucket of white vinegar or a descaling solution approved by the manufacturer.
  4. Open the service ports and circulate the solution through the heat exchanger for the time your manual specifies, usually about an hour.
  5. Drain the solution, then flush with clean water.
  6. Close the service ports, clean the inlet filter, open the isolation valves and purge air from a hot tap before restoring gas and power.

Check your Noritz manual for your model's exact steps. Our guide to descale a tankless water heater covers the job in more detail.

After long periods without use

Noritz's manual warns that on condensing models, the condensate trap must be refilled with water after the heater has been out of use for a long time, so exhaust cannot escape through it. Ask your installer to show you how, or have it done at the next service.

Winter

Freeze protection needs power. See our guide to tankless water heater freeze protection for outages and vacations.

See all codes on our Noritz error codes page.

Common questions

How often should a Noritz tankless be flushed?

About once a year for most homes, and more often with hard water or if a C1 warning appears.

Can skipping maintenance void a Noritz warranty?

Scale damage is commonly excluded from tankless warranties. Keep records of each flush.

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