Noritz Tankless Water Heater Error Code 90: Meaning & How to Fix It

By the ErrorCodePro Editorial Team · Last reviewed October 20, 2026

Noritz tankless water heater error code 90 means: The air supply vent (indoor combustion air), exhaust vent or condensate drain may be clogged, or gas pressure is low. [1] Keep using it? No hot water until it's resolved. Don't keep resetting it.. Start with the owner checks below, beginning with: check the air supply vent.

Smell gas? Leave the building now. Do not touch light switches, phones or appliances inside. Call your gas utility or 911 from outside. CO alarm sounding or headache, dizziness or nausea? Get everyone outside and call 911. Gas valves, burners, venting and wiring are for a licensed technician only. See our safety policy.

Quick facts

Code	90
Also shown as	901, 902
Brand / appliance	Noritz tankless water heater (nrcr condensing tankless water heaters (owner's guide))
System	Venting / airflow
Official meaning	The air supply vent (indoor combustion air), exhaust vent or condensate drain may be clogged, or gas pressure is low. [1]
Keep using it?	No hot water until it's resolved. Don't keep resetting it.
DIY-safe?	Owner checks only (listed below)
Support	Noritz America Technical Support, 1-866-766-7489

On this page: Meaning · Steps · Parts · When to call a technician · Related codes · FAQ

What error code 90 means on a Noritz tankless water heater

The air supply vent (indoor combustion air), exhaust vent or condensate drain may be clogged, or gas pressure is low. [1]

This is a venting / airflow code. Codes and wording can vary by model, so check your owner's manual for your model number.

How to fix Noritz tankless water heater error code 90 (safe owner checks)

Owner checks only: on heating, cooling and water-heating equipment, limit yourself to reading the code and checking the thermostat, breaker and service switch, air filter, condensate drain, that the gas supply valve is open (no disassembly) and that vent terminals are clear of snow or debris. Reset power only if your manual allows it.

Safety first: disconnect power before you remove any panel or reach into the sump or drum. Do not touch wiring, the control board or the motor. If you see water near electrical parts, stop and call a technician. These steps are based on Noritz's published guidance [1], rewritten for clarity.

Check the air supply vent. If combustion air comes from indoors, check the air supply vent for blockage.
Check the exhaust vent. Check the exhaust vent terminal for blockage or obstruction.
Check the condensate drain. On condensing models, make sure the condensate line is draining and isn't clogged or frozen.

Parts that may be involved

Exact parts depend on your model number. This page lists part types only, never part numbers.

No specific part is implied by the manufacturer's guidance for this code.

When to call a technician

Low gas supply pressure: a professional
The code continues: Noritz agent
Gas pressure, gas valve, igniter, flame rod, venting or combustion problems: licensed plumber or gas technician
Gas valves, burners, igniters, flame sensors, venting/flue or CO concerns: licensed HVAC technician or plumber
Refrigerant work: EPA 608-certified technician only
Smell of gas: leave and call the gas utility or 911
Anything involving wiring, the control board, the motor or the water valve electrics
The appliance is under warranty: contact Noritz America Technical Support, 1-866-766-7489 first

Frequently asked questions

What does error code 90 mean on a Noritz tankless water heater?

Noritz lists 90 as follows: The air supply vent (indoor combustion air), exhaust vent or condensate drain may be clogged, or gas pressure is low.

Is it safe to keep using the tankless water heater with 90?

No hot water until it's resolved. Don't keep resetting it..

Can I fix Noritz tankless water heater error 90 myself?

Only with the owner checks on this page, starting with: check the air supply vent. If it persists, call a technician or Noritz America Technical Support, 1-866-766-7489.

Is 901 the same as 90?

Yes. Noritz's documentation lists 901, 902 with the same meaning as 90; the display format depends on the model.

Sources

https://noritz.com/assets/nrcr_ownersguide.pdf (official)

Last reviewed: October 20, 2026. ErrorCodePro is not affiliated with Noritz.