Rinnai Rinnai V65iN Value Series Tankless Water Heater 33 Error Fix: Heating Circuit Sensor Failure

Error code 33 on the Rinnai Rinnai V65iN Value Series Tankless Water Heater means: Heating Circuit Sensor Failure. The space heating circuit temperature sensor has failed. This code applies to RSC combo boiler models only. The RSC series provides both domestic hot water and hydronic space heating through two separate heat exchangers. Error 33 indicates the sensor monitoring the space heating circuit water temperature has malfunctioned. Without this sensor, the boiler cannot regulate the heating circuitwater temperature, which could lead to overheating of the hydronic loop or insufficient heat output. The sensor is located on the heating circuit water outlet. Check the sensor resistance and wiring. Replace the thermistor if faulty. This code does not affect the domestic hot water function — hot water may continue to operate normally while space heating is disabled.

The most successful fix is "Test and Replace the Heating Circuit Temperature Sensor" (medium difficulty, ~45 minutes). Estimated DIY cost: $15-$25. HomeMD has 2 community-ranked fixes for this error.

This error is rated warning severity. It is generally not urgent and can often be resolved with a simple DIY fix.

Yes — the top-ranked community fix ("Test and Replace the Heating Circuit Temperature Sensor") is rated medium difficulty and takes about 45 minutes. Tools needed: T20 Torx screwdriver, Digital multimeter, Needle-nose pliers.

DIY cost: $15-$25. Professional repair typically costs $130-$190. Many homeowners save money by trying the top-ranked community fix first.

The Rinnai Rinnai V65iN Value Series Tankless Water Heater has 8 other known error codes, including: 02 (Ignition Failure), 03 (Bath Fill Function Abnormality), 05 (Blocked Exhaust / Air Supply), 10 (Blocked Exhaust — Air Pressure Switch), 11 (No Ignition), and 3 more.

Error code 33 also appears on 8 other Rinnai models: Rinnai RE180iN RE Series Non-Condensing Tankless Water Heater, Rinnai RL75iN RL Series Tankless Water Heater, Rinnai RL94iN RL Series Tankless Water Heater, Rinnai RSC160iN Condensing Combi Boiler, Rinnai RU130iN Sensei Super High Efficiency Plus Tankless Water Heater, Rinnai RU199iN Sensei Super High Efficiency Plus Tankless Water Heater, and 2 more. The fix may vary by model, so check each model's specific page for tailored repair steps.