Noritz Tankless Water Heater No Hot Water: Error 11, 12

Quick Answer

Noritz water heater not producing hot water: check the display for an error code first - each code points to a specific component. Igniter rod cracked or carbon-tracked (Error 11). For tankless units, annual descaling is critical in hard water areas - scale buildup is the most common cause of reduced output after 2-3 years.

When a Noritz goes cold, it's almost always a battle between air and gas. These units are way more sensitive to pressure drops and intake blockages than a tank heater. If you're seeing Error 11 or 12, the unit tried to light three times and gave up. I've cleared spider webs out of an intake on a Tuesday and had hot water running again in 20 minutes. Don't ignore this one, because repeated failed ignitions stress the gas valve over time and turn a cheap fix into an expensive one.

NoritzWaterheaterSeverity: moderateDifficulty: intermediate75% DIY Success

Time to Fix

15–90 min

Difficulty

intermediate

Parts Cost

—

Tools Needed

Phillips #2 screwdriver, Flathead screwdriver

What Does the NO-HOT-WATER Code Mean?

Diagnosing a Noritz means looking past the plumbing and focusing on the electronics. These are high-performance machines that shut down at the first hint of a combustion problem. Before you tear into the heat exchanger, you need to figure out if the computer is seeing a spark, sensing a flame, or just struggling to breathe. Honestly, most of these calls end up being a dirty sensor or a blocked vent, not some major part failure.

Most Likely Causes

Based on aggregated repair data, here is the probability breakdown for this error code:

Igniter rod cracked or carbon-tracked (Error 11)40%

Vent run exceeding maximum length (Error 12)24%

Burner dirty causing incomplete combustion (Error 90)14%

Gas supply restricted12%

Flame sensor oxidized10%

Symptoms You May Notice

You turn on a hot tap and get cold water, or water starts warm for about 5 seconds then goes cold right as the burner tries to fire up.
Error 11 or Error 12 flashing on the remote controller display, sometimes with a clicking noise as the igniter keeps trying and failing.
The unit makes a spark sound but you never hear the burner actually light, just silence and then the error code appears.
Hot water works fine sometimes and not at all other times, especially on cold mornings when gas pressure tends to dip a bit across the neighborhood.
Water pressure at the hot taps is noticeably lower than the cold side, which usually means the heat exchanger is scaling up and starting to restrict flow internally.

Can you reset a Noritz waterheater to clear the NO-HOT-WATER code?

Hit the power button on the remote controller to turn it off first. Then unplug the unit from the wall and wait a full 60 seconds, not 10 or 15, the full minute so the control board completely clears its memory. Plug back in, power the remote back on, and run a hot tap to trigger a heating cycle. If the same code comes right back within a few seconds, the fault is still physically present and you need to work through the diagnostic steps above.

Tools Required for Diagnosis

Phillips #2 screwdriverFlathead screwdriverMultimeterFlashlight400-grit sandpaper or Scotch-Brite padSoft brush for intake screen cleaningDescaling pump kit (for scale-related faults)Gas manometer (if checking supply pressure)

Diagnostic Checklist

Follow these steps in order. We start with the easiest external fixes before opening up the machine.

Frequently Asked Questions

How much does a Noritz water heater repair cost?

A typical service call runs $150 to $450 depending on what's actually wrong. Cleaning the flame sensor or clearing a blocked intake is usually just the diagnostic fee, maybe $100-150 total. Replacing the igniter rod is around $80-120 in parts plus an hour of labor. Gas valve replacement pushes you toward $400-600 all in. If the heat exchanger is scaled solid, you're looking at $300+ for professional descaling, or a full unit replacement if the exchanger itself is cracked, and that's usually a new unit conversation at that point.

Is it worth repairing or should I just replace it?

Noritz builds these to last 20 years, so if yours is under 12, I'd almost always say repair it. The break-even point is usually around the $600 mark. If a repair is going to cost more than that and the unit is already over 15 years old, the math usually favors a new high-efficiency model because you're getting a fresh warranty and better efficiency too. If the heat exchanger is leaking or scaled up past the point of cleaning, that's a replace situation because exchanger swap labor is brutal on these units.

Can I fix this myself or do I need a pro?

Cleaning the intake filter, descaling with a pump kit, and cleaning the flame sensor are all totally DIY-able if you're comfortable with a screwdriver and following steps carefully. But if you think you've got a gas pressure problem or need to adjust the gas valve manifold pressure, that's a licensed tech job. You need a combustion analyzer and a manometer for that work, and it's genuinely not safe to adjust gas valve settings without the right training and tools. Don't guess on that one.

Why does my Noritz work sometimes but not other times?

Intermittent no-hot-water on a Noritz is almost always the flame sensor. When it's borderline dirty, it'll work when everything is ideal but fail when gas pressure is slightly low, or the unit is cold, or humidity is high. It's cumulative. The sensor is reading just barely enough to keep the board happy under perfect conditions. Clean that sensor first, it's a 10-minute job and it fixes probably 40% of the intermittent calls I go on. Seriously, start there before you chase anything else.

How often should I descale a Noritz tankless water heater?

In a hard water area, anything over 7 grains per gallon, you should flush and descale annually. Soft water areas can stretch to every two or three years. You'll need a descaling pump kit, white vinegar or a commercial descaler like CLR Pro, and about 45 minutes. Skipping this is honestly the number one reason these units develop problems after year three. Scale in the heat exchanger chokes flow, forces the unit to run hotter and longer, and eventually cracks the exchanger, turning a $150 maintenance job into a $1,500 replacement.

Models Known to Experience NO-HOT-WATER Errors

This repair applies to most Noritz waterheaters with this error code. Common model numbers include:

NRC98-DV, NRC66-OD, NRC1111-DV, NRC711-DV, NR98-OD, NR66-OD, NCC199CDV

Written by

Raj Patel

HVAC & Water Systems Specialist · 15 years experience

Last verified for technical accuracy on March 14, 2026