A Noritz has no letter in front of its fault numbers, which is the first thing that separates it from a Navien E-code or a Bosch two-letter code. The number flashes on the wall remote, and on the newer Pro Series units (the EZ and NRCR families) it shows in a display window on the heater itself. Some Pro Series faults carry a third digit: 903 is the venting-specific version of 90, and an exhaust-temperature 94 can read 941 or 942. The remote keeps a history too: switch it off, hold the up and down arrows together until 03 appears, press down once to see 91 followed by the newest code, then step up through 92 and onward until 000 ends the list.
Scale is where people get the brand wrong: LC is a Rinnai maintenance code that a Noritz does not use, and our Rinnai error code guide covers it. A Noritz Pro Series unit flashes C1 followed by a digit when it has detected scale in the heat exchanger, and the alarm only clears once the exchanger has been flushed. Older Noritz models give no early warning at all: the first sign of scale is a 16 or a 20, and by the time a 14 shows up the thermal fuse has already blown. Municipal water in Halton and Hamilton is hard, so these are the codes we see most on units that have gone years without a flush.
Codes vary by model. A 29 can only appear on a condensing unit, 63 and 06 belong to the NRCR with built-in recirculation, and 92 and 93 exist only on models with a built-in neutralizer. Noritz tapes a technical data sheet in a zip bag inside the front cover, and that sheet plus the label on the unit are the authority for your heater: where this page and the label inside the panel disagree, the label wins. The Noritz tankless repair page explains how we approach these units, and ZK Mechanical can talk a code through with you on the phone before anyone drives out.
Noritz tankless water heater codes, decoded
| Code | What it means | Safe? | Try first | When to call |
|---|---|---|---|---|
10 | Combustion abnormality warning. Noritz describes it as the usual precursor to code 90: air or gas flow is low and the heater has cut back its output. | keep running | Look at the intake and exhaust terminations outside for leaves, nests, snow or frost. | Book a visit before it turns into a 90, sooner if the water runs lukewarm. |
11 | Ignition failure. There is a demand for hot water but the burner did not light, or it lit and the flame rod never saw it. | turn it off | Confirm the gas valve under the heater is open and other gas appliances work. Power-cycle once. | If 11 returns after one reset. Spark, gas pressure and flame rod checks need a manometer. |
12 | Flame loss. The burner lights, then the flame goes out during operation. | turn it off | Check that nothing is blocking the vent termination and that the exhaust is not being drawn back into the intake. | Same day if it repeats. Low gas pressure and a dirty flame rod are the usual finds. |
14 | Thermal fuse has opened after a significant overheat of the heat exchanger. The fuse cannot be reset once it trips. | turn it off | Nothing. Leave the power off. | Yes. Noritz recommends replacing the fuse and the heat exchanger together. |
16 | Abnormally high outlet temperature. The heater restricts its own water flow as a precaution. | turn it off | Unplug the heater for 20 seconds and plug it back in. Test at a tap carefully: the water may be very hot. | If it comes back. Scale in the heat exchanger is the common cause. |
20 | High limit switch tripped. Depending on the model the switch opens at 80, 94 or 96°C, and combustion stops at once. | turn it off | A hard reset by disconnecting power clears it once. Do not keep resetting. | If it trips twice. Scale, poor combustion or a failed switch all need testing. |
29 | Condensate is not draining from a condensing unit: a blocked, frozen or badly sloped drain line, including a neutralizer in that line that has plugged up. | turn it off | Follow the plastic drain tube and straighten any kink. In a cold snap, check where it runs through an unheated space. | If the line looks clear and 29 stays. The drain path and neutralizer need opening up. |
31, 32, 33 | Thermistor faults: 31 is the cold water sensor, 32 the hot water sensor, 33 the heat exchanger outlet sensor. | turn it off | Nothing inside the cabinet is a homeowner job. | Book a repair. The sensor or its harness connection is tested with a meter. |
61 | Fan motor abnormality. The fan is not turning, or is turning well outside the speed the board expects. | turn it off | Check the vent termination for a blockage, then power-cycle once. | If the fan is silent, noisy, or the code repeats. |
65, 66 | Water servo faults: 65 is the main water control servo, 66 is the bypass servo that blends the outlet temperature. | turn it off | None. | Book a repair. A sticking servo is often scale or debris. |
71 | Gas valve abnormality: the circuit board cannot drive the gas valve solenoids properly. | turn it off | If the heater is fed from a battery backup, generator or inverter, plug it into a regular wall outlet and retry. | If it persists on clean utility power. |
72 | Flame rod circuit abnormality: the heater detects flame before ignition, when no flame should be present. | call now | Switch the heater off, close the gas valve beneath it and leave both alone. | Immediately. A flame signal with the burner off is not one to reset past. |
73 | Circuit board setting fault. A dipswitch or jumper was changed with the power on, or a replacement board was never programmed. | turn it off | Unplug for 30 seconds and plug back in. | If it appeared right after a board or control was replaced. |
90 | Combustion abnormality. The fuel and air mixture is out of specification and the burner is not burning cleanly. | turn it off | Clear the outside terminations and the intake screen on the front cover. Nothing more. | Same day. Gas pressure, venting, dipswitch settings and a dirty fan or burner are all on the list. |
92, 93 | Built-in condensate neutralizer life: 92 is the first warning that it is near the end, 93 means it has reached it and output may be reduced. | keep running | None. Note which of the two numbers is showing. | Book a neutralizer replacement. The timer is reset as part of the job. |
94 | Exhaust temperature too high on a condensing unit. Normal condensing exhaust is cool enough for plastic vent pipe. | turn it off | Leave it off. Do not run a condensing heater that is overheating plastic venting. | Yes, before it runs again. |
C1 + digit | Scale build-up alarm on Pro Series (premix) models. The code stays until the heat exchanger has been flushed. | keep running | Nothing clears it at the remote. | Book a descale flush. Noritz does not cover scale damage under warranty. |
The codes that usually mean a real repair
C1, 16 or 20: scale in the heat exchanger
Scale insulates the inside of the heat exchanger, so the metal runs hotter than the water it is heating and the temperature codes follow. Caught at the C1 or first-16 stage, the fix is a descale flush at $150–$300, with the inlet filter cleaned and the ignition and flame rods checked in the same visit. Left until a 14, the thermal fuse has opened and Noritz's own guidance is to replace the fuse and the heat exchanger together, which is hours of labour and a written quote rather than a flat figure.
11 or 12: ignition rod, flame rod and gas supply
Noritz frames ignition as three ingredients, air, gas and spark, and on a tankless you can nearly always rule out air. The visit comes down to cleaning the ignition and flame rods, checking the ground, and measuring inlet gas pressure with the burner at full fire. Most of these repairs fall inside the usual $150–$800 range, but if the pressure collapses under load, the gas line is too small for the heater and upsizing the run can add $400–$1,200. Our page on Noritz error code 11 walks through that diagnosis in order.
10 or 90: venting, fan and burner cleaning
On a new install, 90 usually traces to gas pressure, vent length or dipswitches set for the wrong elevation or pipe size. On a heater that has run for years it is more often dirt: lint on the fan and venturi, a blocked intake screen, or a condensate line that will not drain. The diagnostic visit is $90–$150 and is folded into the repair if you go ahead. Noritz error code 90 has the longer explanation of why the heater cannot reach its set temperature.
Licensed technicians, a written price before the repair, no overtime charges.
Common questions
How do I reset a Noritz tankless water heater after an error code?
Cut the power, wait and restore it: unplug the cord or switch off the breaker, then open a hot tap to test. Noritz gives 20 seconds for a 16 and 30 seconds for a 73, and code 20 needs the same hard reset. Do it once only, because a code that reappears is describing a real fault, and never reset a 72. If you need hot water today, our tankless water heater repair service is the next step.
Does a Noritz show an LC code when it needs descaling?
No: LC0 through LC9 are Rinnai codes. A Noritz Pro Series unit flashes C1 followed by a digit when it detects scale, and that alarm clears only after the heat exchanger is flushed. Older Noritz models have no scale alarm, so the warning arrives late as a 16 or a 20. If a website lists LC as a Noritz code, check it against the data sheet inside your front cover.
Can I keep using hot water with code 10 or code 90 showing?
With a 10, yes for a short while: the heater is still firing at reduced output and telling you combustion is drifting. Check the outdoor terminations and book service. With a 90, stop. The burner is no longer burning cleanly, the heater has shut itself down for that reason, and repeated resets only push more gas through a dirty or starved burner.
Why does my Noritz throw code 71 only when the power is out?
Because of what is feeding it. Noritz notes that 71 is common where the heater runs from a battery backup or another alternative supply that does not produce a pure sine wave: the circuit board cannot drive the gas valve properly on that power. A circuit shared with another appliance can cause the same disturbance. Run the heater from a normal outlet and see whether the code stays away before paying for parts.
What does a Noritz tankless repair cost?
A diagnostic visit is $90–$150 and is credited toward the repair if you proceed. Most tankless repairs land between $150 and $800 depending on the part, and a descale flush on its own is $150–$300. A heat exchanger replacement after a 14 is quoted in writing, and on an older heater we will put that quote beside the price of a new unit so you can compare.