Rinnai tankless error code 33 indicates a high heat exchanger outlet temperature, usually pointing to insufficient water flow or scale buildup.
Table of Contents
- What does error code 33 mean on a Rinnai tankless water heater?
- Why is my Rinnai water heater showing error code 33?
- How do I perform quick fixes for Rinnai error code 33?
- What advanced steps should I take if the error returns?
- Which fix matches your specific symptom?
- When should I stop troubleshooting and call a technician?
- What information should I have ready before calling for service?
- How can I prevent Rinnai error code 33 from coming back?
What does error code 33 mean on a Rinnai tankless water heater?
Error code 33 indicates that the heat exchanger outlet temperature has exceeded normal operating limits, triggering an automatic safety shutdown.
When the internal sensors detect excessive heat at the outlet, the unit stops heating to prevent permanent damage to internal components. This safety feature protects the system from overheating, but it points to an underlying restriction in water movement or a sensor malfunction.
- Sensors detect abnormally high water temperatures at the heat exchanger outlet.
- The appliance immediately shuts down burners to prevent severe thermal damage.
- This error code is standard across most Rinnai tankless water heater models.
- It frequently correlates with hard water scale accumulation inside the heat exchanger.
- Low water flow rates can also cause heat to concentrate excessively in the exchanger.
Why is my Rinnai water heater showing error code 33?
The most common causes are mineral scale buildup in the heat exchanger, restricted water flow, or a failing thermistor sensor.
Over time, minerals from tap water precipitate inside the copper tubing, creating an insulating layer that traps heat. Additionally, anything that slows down water flow prevents the system from efficiently dissipating thermal energy during normal operation.
- Heavy mineral scale buildup restricts water transfer and traps excessive heat.
- Clogged inlet water filter screens significantly reduce incoming flow rate.
- A malfunctioning outlet thermistor reads high temperatures incorrectly.
- Closed or partially closed water supply valves restrict necessary volume.
- Venting obstructions can sometimes alter internal combustion dynamics and heat transfer.
How do I perform quick fixes for Rinnai error code 33?
Clean the inlet filter and reset the system before attempting any advanced descaling or component testing procedures.
Always turn off the power at the wall switch or circuit breaker before touching internal or external plumbing components. Safety is paramount when dealing with electrical and water connections on tankless water heating systems.
- Turn off the power switch on the water heater and unplug the unit.
- Locate the cold water inlet filter screen at the bottom of the unit.
- Unscrew and remove the filter screen to inspect for debris and scale.
- Rinse the filter thoroughly under clean running water to remove clogs.
- Reinstall the filter securely, restore power, and reset the error code.
What advanced steps should I take if the error returns?
Flush the heat exchanger with a descaling solution or inspect the thermistor sensors for proper electrical resistance.
If basic cleaning does not resolve the high-temperature fault, mineral deposits inside the copper coils likely require a thorough chemical flush. Alternatively, diagnostic testing of the temperature sensors may reveal a faulty component requiring replacement.
- Shut off the gas supply valve and unplug the water heater completely.
- Connect isolation valve hoses to a submersible utility pump and descaling bucket.
- Circulate food-grade white vinegar through the heat exchanger for forty-five minutes.
- Flush the system thoroughly with clean water before disconnecting the hoses.
- Test sensor wiring connections and replace any damaged thermistors if necessary.
Which fix matches your specific symptom?
Match your operational symptoms to the corresponding causes and recommended immediate actions in this reference table.
Different operational scenarios produce error code 33 under varying conditions. Use this quick reference guide to identify the precise remedy required for your specific household water heating situation.
| Symptom | Likely cause / fix |
|---|---|
| Code appears during high flow | Inlet filter clogged; clean screen. |
| Code appears intermittently | Scale buildup; flush heat exchanger. |
| Code appears instantly on startup | Faulty thermistor; check sensor wiring. |
| Low hot water pressure overall | Restricted water supply; open valves fully. |
When should I stop troubleshooting and call a technician?
Call a licensed professional if descaling fails, gas components are involved, or electrical wiring shows visible damage.
Gas appliances require extreme caution, and any manipulation of gas valves, burners, or sealed combustion chambers must be handled by certified experts. Stop immediately if you smell gas or if troubleshooting steps do not clear the safety fault.
- Stop immediately and shut off the gas supply if you smell gas.
- Call a professional if the error code persists after a complete descaling.
- Seek certified help for internal electrical wiring or control board issues.
- Contact support if replacement parts like thermistors or gas valves are needed.
What information should I have ready before calling for service?
Gather your exact appliance model number, serial number, warranty details, and a record of troubleshooting steps tried.
Having precise appliance details ready helps customer support or service technicians diagnose the issue faster. Note the exact conditions under which error code 33 occurs to assist the technician during the service visit.
- Locate the rating plate on the side of the unit for the exact model number.
- Write down the serial number to verify active manufacturer warranty status.
- Note whether the error happens during high water flow or low water flow.
- Summarize the cleaning and descaling steps you have already performed.
How can I prevent Rinnai error code 33 from coming back?
Install a whole-house water softener and schedule annual heat exchanger flushing to prevent mineral scale accumulation.
Proactive maintenance is the most effective way to protect tankless water heaters from thermal errors. Hard water minerals deposit rapidly in high-heat environments, making routine preventative care essential for long-term reliability.
- Install a water softening system if your home has hard water.
- Perform an annual chemical flush of the heat exchanger coils.
- Inspect and clean the cold water inlet filter every six months.
- Avoid running multiple high-demand hot water fixtures simultaneously if flow is restricted.
Frequently Asked Questions
Can I reset error code 33 without fixing the underlying problem?
You can clear the error temporarily by turning the unit off and on, but error code 33 will return if the high heat condition remains unaddressed. The safety mechanism triggers for a valid reason to protect the internal components from overheating.
Is error code 33 dangerous to my home?
Error code 33 itself is a safety lockout designed to prevent danger by shutting down the burners when overheating occurs. However, ignoring the root cause, such as severe scale buildup or gas valve issues, can lead to permanent equipment failure.
How often should I descale my Rinnai tankless water heater?
You should descale your tankless water heater at least once a year in areas with hard water. If you live in an area with extremely high mineral content in your municipal supply, flushing every six months may be necessary to prevent error code 33.
What tools do I need to flush the heat exchanger myself?
To flush the system, you need a small submersible transfer pump, two short washing machine hoses, a 5-gallon bucket, and food-grade white vinegar. Always disconnect electrical power and shut off the gas supply before starting maintenance.
What should I do if error code 33 appears right after installation?
If error code 33 appears on a newly installed unit, check that all water supply valves are fully open and that packing material was removed from the pipes. Sometimes air pockets or closed service valves restrict flow and cause immediate high-temperature lockouts.
Bottom Line
Start by inspecting and cleaning the cold water inlet filter, as this quick step resolves many restricted flow issues. If the error code persists, plan to descale the heat exchanger or contact a qualified technician for assistance.
Sources
- Rinnai Owner’s Manual
- Rinnai Installation Manual
- Manufacturer Support Page