Rheem tankless error code 33 typically indicates an exhaust temperature that is too high, often caused by restricted venting or improper combustion airflow.
Table of Contents
- What does error code 33 mean on a Rheem tankless water heater?
- Why is my Rheem water heater showing error code 33?
- How do I perform quick fixes for Rheem error code 33?
- What are the next troubleshooting steps if error code 33 persists?
- Which fix matches your specific Rheem water heater symptom?
- When should I stop troubleshooting and call a technician?
- What information should I have ready before calling a technician?
- How can I prevent Rheem error code 33 from returning?
What does error code 33 mean on a Rheem tankless water heater?
Error code 33 on a Rheem tankless water heater indicates an excessively high exhaust gas temperature detected by the unit’s internal sensors.
Tankless water heaters monitor internal and exhaust temperatures closely to prevent internal damage or hazardous overheating. When the exhaust temperature crosses safety thresholds, the system immediately shuts down combustion and displays code 33 to prevent further damage.
- The exhaust temperature sensor has detected a temperature higher than normal operating parameters.
- Combustion gases are not exiting the flue quickly enough, causing heat to build up inside.
- Incorrect fuel conversion or improper gas pressure can cause excessively hot combustion output.
- Intake air supply might be restricted, forcing the unit to run hotter than intended.
- Confirm your exact model’s manual, as error code meanings can slightly vary by production year.
Why is my Rheem water heater showing error code 33?
Common causes for error code 33 include blocked venting pipes, intake air obstructions, scale buildup, or incorrect gas pressure adjustments.
When proper airflow is compromised, heat accumulates inside the heat exchanger and venting assembly. Identifying the source of the blockage or heat retention is essential before attempting any physical resets or component inspections.
- Blocked, crushed, or improperly installed exhaust venting pipes restricting natural heat dissipation.
- Debris, nests, or leaves blocking the outdoor intake or exhaust termination cap.
- Severe scale buildup inside the heat exchanger reducing thermal transfer efficiency.
- Excessive incoming gas pressure forcing a hotter burn than the system is designed to handle.
- A malfunctioning or degraded exhaust thermistor sensor sending incorrect high temperature readings.
How do I perform quick fixes for Rheem error code 33?
Safely clear error code 33 by inspecting venting paths, checking air intake screens, and performing a simple power reset.
Before calling a professional, ensure that the unit is powered down safely and that external venting obstructions are cleared. Always turn off the electrical power breaker before touching any internal or external components.
- Turn off the power switch on the water heater and turn off the dedicated circuit breaker.
- Inspect the outdoor exhaust and intake termination vents for bird nests, leaves, or snow blockages.
- Check that all indoor venting sections are securely connected, uncrushed, and completely free of leaks.
- Wait five minutes to let internal sensors cool down completely before restoring power.
- Turn the circuit breaker and unit power back on, then open a hot water tap to test operation.
What are the next troubleshooting steps if error code 33 persists?
Advanced troubleshooting involves checking gas pressure levels, inspecting the exhaust thermistor sensor, and flushing the heat exchanger.
If basic venting checks and power resets fail to clear code 33, the underlying issue likely involves internal sensor readings or water scale accumulation. Because gas appliances involve combustible fuel, proceed carefully and adhere strictly to safety rules.
- Unplug the appliance or turn off the gas supply valve before inspecting internal wiring or gas components.
- Inspect the exhaust thermistor sensor wiring harness for loose connections, corrosion, or heat damage.
- Measure the incoming gas supply pressure using a manometer to verify it matches manufacturer specifications.
- Perform a standard system flush using vinegar and a descaling pump to remove mineral scale from the heat exchanger.
- Test sensor resistance with a multimeter if you suspect a failing thermistor component.
Which fix matches your specific Rheem water heater symptom?
Match your immediate observation to the corresponding likely cause and recommended corrective action for error code 33.
Different symptoms point directly toward specific underlying failures. Use this reference table to quickly isolate whether your issue stems from blocked airflow, scale, or a faulty sensor component.
| Symptom | Likely cause / fix |
|---|---|
| Error appears immediately on startup | Blocked exhaust vent / Clear outdoor vent |
| Error appears after running hot water | Scale buildup / Flush heat exchanger |
| Code returns after power reset | Faulty thermistor / Replace sensor |
| Loud roaring sound during combustion | High gas pressure / Call licensed pro |
When should I stop troubleshooting and call a technician?
Stop immediately and call a licensed professional if you smell gas, detect combustion leaks, or need to service gas valves.
Gas appliances present severe safety risks including carbon monoxide poisoning and explosion hazards. Any work involving gas valve adjustments, sealed combustion chambers, or complex electrical diagnosis must be performed by a certified technician.
- Stop immediately and shut off the main gas supply if you notice any unusual gas odor.
- Call a professional if error code 33 persists despite clear venting and a clean heat exchanger.
- Never attempt to adjust or repair gas control valves or internal gas regulators yourself.
- Contact a certified technician if electrical components or control boards show signs of burn damage.
- Reach out to your local gas utility immediately if a gas leak is suspected anywhere near the appliance.
What information should I have ready before calling a technician?
Gather your exact water heater model number, serial number, warranty details, and a record of troubleshooting steps tried.
Having accurate information ready speeds up diagnosis and ensures the service technician brings the correct replacement parts. Check the metal rating plate affixed to the side of your Rheem tankless water heater cabinet for details.
- Locate the exact model number and serial number printed on the side sticker of the water heater.
- Note the purchase date or installation date to verify whether the unit is still under manufacturer warranty.
- Write down a clear timeline of when error code 33 first appeared and under what water usage conditions.
- List all troubleshooting steps you have already performed, such as power resets or vent inspections.
- Keep your owner’s manual handy to reference specific error code tables and part diagrams.
How can I prevent Rheem error code 33 from returning?
Prevent future occurrences of error code 33 by scheduling annual professional maintenance, flushing scale, and checking vents.
Routine preventive maintenance ensures peak operating efficiency and extends the lifespan of your tankless water heater. Keeping air intake paths and heat exchangers clean prevents dangerous thermal buildups.
- Schedule an annual professional inspection of your water heater venting system and combustion chamber.
- Flush the heat exchanger with a descaling solution every twelve to eighteen months to prevent mineral buildup.
- Inspect outdoor intake and exhaust termination caps seasonally to ensure no blockages have accumulated.
- Keep surrounding indoor areas clean and free of dust, lint, or chemical vapors that can enter the intake.
- Confirm that your water filtration system is operating correctly to minimize hard water scale deposits.
Frequently Asked Questions
Can I clear Rheem error code 33 by just resetting the power?
Resetting power can temporarily clear the display if it was a false positive reading caused by a transient temperature spike. However, if the underlying exhaust blockage or high temperature condition remains, error code 33 will quickly return.
Is error code 33 safe to ignore if the water heater still produces hot water?
No, you should never ignore error code 33. It indicates that exhaust temperatures have exceeded safe operating limits, which risks damaging internal components or creating dangerous venting conditions.
What tools do I need to troubleshoot a Rheem tankless water heater?
Basic troubleshooting requires safety glasses, work gloves, and a flashlight to inspect venting. Advanced checks may require a digital multimeter for testing sensors and a manometer for verifying incoming gas pressure.
How often should I flush my Rheem tankless water heater to prevent errors?
You should flush your tankless water heater at least once a year in standard water conditions, or every six months if you live in an area with hard water to prevent scale-induced errors.
Does Rheem warranty cover repairs related to error code 33?
Rheem warranties typically cover defective parts like heat exchangers or sensors, but they generally exclude service labor fees and failures caused by poor installation, venting blockages, or lack of maintenance.
Bottom Line
Always turn off the power breaker before inspecting your Rheem tankless water heater. Inspect your outdoor venting for blockages first, and call a licensed professional if gas valves or internal combustion components require service.
Sources
- Rheem owner’s manual
- Rheem installation manual
- Manufacturer support page