Noritz error code 33 typically indicates an abnormal exhaust temperature or potential overheating issue that requires checking your venting system and water flow.
Table of Contents
- What does error code 33 mean on a Noritz water heater?
- Why is my Noritz unit overheating and showing code 33?
- How can I safely perform quick fixes for Noritz error code 33?
- What are the next troubleshooting steps if the error returns?
- Which troubleshooting step matches your specific symptom?
- When should you stop troubleshooting and call a professional?
- What information should you prepare before calling a technician?
- How can you prevent Noritz error code 33 from returning?
What does error code 33 mean on a Noritz water heater?
Noritz error code 33 indicates an abnormally high exhaust temperature detected by the unit’s thermistor.
Tankless water heaters monitor internal temperatures closely to prevent damage to the unit and surrounding structures. When the exhaust gas sensor detects excessive heat, the system shuts down burners as a safety precaution. Because exact threshold temperatures can vary slightly by model line and installation year, always consult your owner’s manual or the manufacturer support page to confirm precise specifications.
- The exhaust temperature sensor has detected excessive heat inside the venting pathway.
- Blocked intake or exhaust vents can trap heat and trigger this safety shutdown.
- Insufficient water flow through the heat exchanger may cause rapid internal overheating.
- Scale buildup inside the heat exchanger restricts proper heat transfer and raises exhaust temperatures.
- A failing exhaust thermistor or loose wiring harness can report false high-temperature readings.
Why is my Noritz unit overheating and showing code 33?
This error is most commonly caused by restricted airflow, blocked venting, or low water flow rates.
When a tankless water heater cannot vent properly or circulate water efficiently, thermal energy builds up rapidly. Over time, mineral scale deposits can insulate the water inside the pipes, forcing the burner heat out through the exhaust rather than into the water. Additionally, external blockages on roof caps or sidewall terminations prevent hot combustion gases from escaping quickly.
- Debris, bird nests, or ice buildup obstructing the outdoor vent termination cap.
- Heavy limescale accumulation coating the interior walls of the heat exchanger.
- Water filter screen clogged with sediment, severely reducing the incoming flow rate.
- Improper vent pipe installation or excessive total vent length exceeding manufacturer limits.
- Gas supply pressure set too high, causing excessive burner output and overheating.
How can I safely perform quick fixes for Noritz error code 33?
Perform a hard reset, inspect the water filter screen, and check the venting path.
Before touching any internal components, always turn off the power switch and unplug the unit or shut off the dedicated circuit breaker. Gas appliances require extreme caution; never attempt to service gas valves, gas lines, or sealed burner assemblies yourself. If you smell gas at any time, immediately evacuate the area, leave the door open, and call your gas utility provider or a licensed professional.
- Turn off the power switch located on the front of the water heater and unplug the unit.
- Locate and remove the cold water inlet filter screen to check for trapped debris or sediment.
- Rinse the water filter screen thoroughly under clean running water before reinstalling it securely.
- Inspect the outdoor intake and exhaust vent terminals to ensure they are completely clear of obstructions.
- Plug the unit back in, turn the power switch on, and run a hot water faucet to test.
What are the next troubleshooting steps if the error returns?
Flush the heat exchanger with a descaling kit to remove mineral buildup.
If basic resets and filter cleanings do not clear Noritz error code 33, mineral scaling inside the heat exchanger is the most likely culprit. Hard water minerals insulate the water pathways, causing internal temperatures to spike quickly. Flushing the system with food-grade white vinegar using a submersible pump helps restore normal heat transfer and operational efficiency.
- Turn off the power switch and unplug the water heater from the electrical outlet.
- Shut off the hot and cold water isolation valves connected to your tankless water heater.
- Attach descaling hoses to the service ports and place the pump into a bucket filled with white vinegar.
- Open the service port valves and run the circulation pump continuously for at least 45 minutes.
- Flush the system thoroughly with clean water, close the service ports, and reopen the water supply valves.
Which troubleshooting step matches your specific symptom?
Review this quick reference table to match your exact symptom with the correct diagnostic action.
Different underlying issues can trigger similar error codes on your water heater. Use this symptom guide to quickly identify whether your problem stems from restricted water flow, venting obstructions, or electrical sensor faults.
| Symptom | Likely cause / fix |
|---|---|
| Error appears immediately on startup | Faulty thermistor or loose wiring harness. |
| Error occurs during high hot water demand | Scale buildup; flush heat exchanger. |
| Weak hot water pressure with error | Clogged cold water inlet filter screen. |
| Venting pipe feels excessively hot | Blocked exhaust vent termination cap. |
| Error code returns after hard reset | Call licensed technician for gas valve check. |
When should you stop troubleshooting and call a professional?
Stop immediately and call a licensed technician if you detect gas odors or electrical component failures.
While basic maintenance like cleaning filters and descaling can be handled by homeowners, gas appliances carry inherent risks. You must call a professional if troubleshooting steps fail to resolve error code 33, or if you suspect issues with gas pressure, combustion chambers, or internal wiring boards. Never attempt repairs on gas valves or sealed combustion systems yourself.
- You notice any smell of natural gas or propane near the appliance.
- Error code 33 persists immediately after a complete heat exchanger flush.
- Electrical components, control boards, or wiring harnesses show signs of burning or damage.
- The outdoor venting configuration violates manufacturer installation clearances.
- You feel uncomfortable or unsure about performing any step of the diagnostic process.
What information should you prepare before calling a technician?
Have your complete unit model number, serial number, and warranty details ready.
Providing accurate information when contacting customer support or a local plumbing professional speeds up diagnosis and ensures the technician brings the correct replacement parts. Note down the exact error code behavior and any troubleshooting steps you have already attempted.
- The exact model number and serial number printed on the side rating plate.
- The date of installation and proof of original purchase for warranty verification.
- A clear description of when error code 33 appears during water heater operation.
- A summary of all troubleshooting steps you have already performed.
- Your contact information and preferred service window.
How can you prevent Noritz error code 33 from returning?
Perform annual water heater flushing and regular filter inspections to prevent future overheating.
Proactive maintenance is the best way to keep your Noritz tankless water heater running efficiently for years. Hard water regions require more frequent descaling to prevent mineral accumulation inside the heat exchanger coils. Keeping intake and exhaust pathways completely clear ensures safe combustion airflow at all times.
- Schedule an annual heat exchanger flush, especially if your home has hard water.
- Inspect and clean the cold water inlet filter screen every six months.
- Check outdoor vent terminals seasonally to ensure no leaves or debris block airflow.
- Test water pressure regulators to make sure incoming household pressure remains stable.
- Review the owner’s manual periodically for recommended maintenance intervals.
Frequently Asked Questions
Can I still use hot water when my Noritz water heater shows error code 33?
No, error code 33 is a safety lockout that shuts down burner operations to prevent overheating damage. The unit will typically not fire up or provide hot water until the underlying high-temperature condition is resolved and the error is cleared.
What should I do if error code 33 appears right after a power outage?
Power surges or sudden outages can sometimes confuse the digital control board. Try performing a hard power reset by turning off the front power switch, unplugging the unit for sixty minutes, and plugging it back in to restore normal sensor calibration.
Is Noritz error code 33 covered under the manufacturer warranty?
Component failures like a defective thermistor or heat exchanger leaks may be covered depending on your warranty terms and installation date. However, service visits for routine maintenance, descaling, or external venting blockages are generally not covered.
How often should I descale my Noritz tankless water heater to prevent this error?
For homes with moderately hard water, descaling should be performed at least once a year. If you live in an area with very hard water, you may need to flush the heat exchanger every six months to prevent mineral scale buildup.
Why does the error code return immediately even after I cleaned the filter?
If cleaning the inlet filter does not work, the internal exhaust thermistor may be failing or heavy scale might be trapped deep inside the heat exchanger coils. A professional technician should test the sensor resistance and inspect internal components.
Bottom Line
Turn off the power switch, unplug your water heater, and inspect the cold water inlet filter screen as your first step. If the error persists, contact a licensed professional for assistance.
Sources
- Noritz Owner’s Manual
- Noritz Technical Support Guide
- Manufacturer Support Page