Short answer
Read the code on the remote first. Noritz says code 11 means ignition failure, 12 a flame that will not stay lit, 16 a temperature spike usually tied to scale, 29 a condensate drain problem and 90 a combustion fault. No code and no hot water often means flow is below the 0.5 GPM needed to start.
Key facts
- Noritz says its units need a minimum flow of 0.5 GPM to activate; below that, the heater does not fire and shows no code.[2]
- Noritz's standard residential warranty is 12 years on the heat exchanger, 5 years on parts and 1 year of approved labor; EZ series units installed from 2019 carry 25 years on the heat exchanger.[1]
- Noritz's warranty excludes damage from water harder than 12 grains per gallon (200 mg/L).[1]
First: is it safe to troubleshoot?
Most Noritz units are gas-fired. If you smell gas, do not touch the unit, switches or a phone inside. Leave and call the gas utility or 911 from outside. See gas smell near the water heater.
This page is a neutral, symptom-based guide. We are not affiliated with Noritz and we do not repair water heaters.
The common Noritz codes, in Noritz's words
Noritz units show a number on the remote controller when they detect a fault. These are the codes Noritz itself describes as most common:
| Code | What Noritz says it means | Likely causes Noritz lists | Who fixes it |
|---|---|---|---|
| 11 | Ignition failure; air, spark or gas is missing | Gas off or low, empty propane tank, airflow problem, debris on the ignition plug | Homeowner checks gas is on; pro for the rest[2][3] |
| 12 | Flame lights but will not stay lit | Low gas pressure or airflow; low propane tank volume | Licensed plumber[2][3] |
| 16 | Sharp spike in outlet water temperature | Scale buildup reducing heat transfer | Descaling, often by a pro[3] |
| 29 | Condensate drainage problem (condensing units) | Blocked or wrongly piped condensate drain | Licensed plumber[3] |
| 73 | Circuit board settings error | Settings changed with power on, or a mis-set board | Unplug 30 seconds, then a pro if it returns[3] |
| F76 | Communication failure between linked units | More than one remote on Quick-Connected units | Check remotes, then a pro[3] |
| 90 | Combustion abnormality, poor air and fuel mix | Low gas supply, vent blockage, debris in the fan | Licensed plumber[2][3] |
Noritz's own fix steps for 11, 12 and 90 call for measuring gas pressure with a digital manometer and testing the igniter with a meter[2]. Those are jobs for a licensed plumber with the right tools, not homeowner steps.
No code, no hot water
Noritz notes a case that shows no code at all: you open a hot tap and get cold water. If demand is below the minimum flow of 0.5 GPM, the unit never fires[2]. Things to try:
- Open the hot tap fully, or run two hot taps at once.
- Clean any aerator on the faucet you are using.
- Check that the water shutoff valves at the heater are fully open.
If a strong flow still gets no heat, Noritz suggests contacting its support to work through keypad diagnostics[2]. See no hot water from a tankless heater for more on flow-related causes.
Scale: the problem behind many repairs
Code 16 is the one Noritz ties directly to scale[3]. HomeGuide calls skipped flushing the number one cause of breakdowns in tankless systems, and recommends flushing and descaling at least once a year, more often in hard water[4].
Hardness also matters for warranty. Noritz's warranty excludes damage from water harder than 12 grains per gallon (200 mg/L)[1]. If your water is that hard, ask a pro about treatment before scale becomes a heat exchanger claim. See hard water and your water heater.
What a homeowner can safely check
- Write down the code before resetting anything.
- Confirm the gas is on, other gas appliances work, and a propane tank is not low.
- Confirm power to the unit and that the water valves are open.
- Make sure the outdoor vent terminal is clear of snow, leaves or nests.
- For code 73 only, unplug for 30 seconds and plug back in, as Noritz describes[3].
Do not remove the front cover. Gas valves, burners, igniters, fans, boards and the heat exchanger are all behind it and need a licensed plumber.
Warranty basics from Noritz's own page
- Heat exchanger. For single-family homes, 12 years on units installed from September 1, 2010. EZ series units installed from January 1, 2019 carry 25 years, or 15,000 burn hours, whichever comes first[1].
- Parts and labor. 5 years on defective parts other than the heat exchanger, and 1 year of approved reasonable labor[1].
- When it starts. On the date of installation by a Noritz Authorized Installer, or 30 days after purchase, whichever comes first[1].
- Recirculation. An aquastat is the minimum pump control needed to keep the full recirculation warranty[1].
- Transfer. The warranty covers the original buyer only and ends on transfer[1].
- Claims. Noritz lists 866-766-7489 and [email protected][1]. Have the model, serial number and install date ready. To estimate age from the serial number, try our age decoder.
Repair costs
HomeGuide's national ranges, published August 2025[4]:
| Service | Typical range |
|---|---|
| Tankless repair, average | $300 to $1,300 |
| Flush and descale | $75 to $300 |
| Heat exchanger replacement | $600 to $1,300 |
Service call fees of $50 to $200 may apply[4]. These are not quotes. In the first year, Noritz's labor coverage may offset part of a covered repair[1].
HomeGuide puts tankless lifespan at 10 to 20 years and suggests replacement when a repair costs more than 50% of a new unit[4]. A heat exchanger failure outside warranty on an older unit is the usual tipping point.
When to call a pro
- Codes 11, 12 or 90 that return after you confirm the gas is on.
- Code 29 or any water dripping from the cabinet.
- Code 16, or a unit in hard water that has not been descaled in a year or more.
- Any code that returns after a reset, or any work behind the front cover.
More questions
Can I clear a Noritz code by turning the power off and on?
For code 73, a circuit board settings error, Noritz says to unplug the heater for 30 seconds and plug it back in. For ignition, flame and combustion codes, a reset only hides the cause. If the code returns, call a pro.
Does my Noritz warranty transfer if I sell the house?
No. Noritz's warranty page says the warranty is for the original buyer only and ends when the product is transferred to anyone else.
Sources
- Product registration and warranty terms, Noritz America. Accessed 2026-10-06.
- Common Noritz tankless error codes: updated (Jun 6, 2022), Noritz America. Accessed 2026-10-06.
- How to resolve the seven most common Noritz tankless error codes (Nov 16, 2015), Noritz America. Accessed 2026-10-06.
- Hot water heater repair cost (Aug 7, 2025), HomeGuide. Accessed 2026-10-06.
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