Rinnai Rinnai RU199iN Sensei Super High Efficiency Plus Tankless Water Heater 72 Error Fix: Flame Detection Circuit Fault

Error code 72 on the Rinnai Rinnai RU199iN Sensei Super High Efficiency Plus Tankless Water Heater means: Flame Detection Circuit Fault. The flame detection (flame rod) circuit on the control board has a fault. The flame sensing circuit measures the ionization current produced when the flame rod is immersed in the burner flame. This extremely small current (microamps) is amplified by the control board to determine whether flame is present. Error 72 indicates the sensing circuit on the board is malfunctioning — it may be reporting flame when none exists or failing to detect a valid flame signal. First, check the flame rod and its wiring — disconnect the flame rod wire from the board, clean the flame rod and rod insulator, verify the ground path, and reconnect. If error 72 persists, the amplifier circuit on the control board has failed and the board needs replacement.

The most successful fix is "Test Flame Rod Circuit and Replace Control Board if Faulty" (hard difficulty, ~60 minutes). Estimated DIY cost: $0-$20. HomeMD has 2 community-ranked fixes for this error.

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

Yes — the top-ranked community fix ("Test Flame Rod Circuit and Replace Control Board if Faulty") is rated hard difficulty and takes about 60 minutes. Tools needed: T20 Torx screwdriver, Multimeter, Needle-nose pliers.

DIY cost: $0-$20. Professional repair typically costs $350-$500. Many homeowners save money by trying the top-ranked community fix first.

The Rinnai Rinnai RU199iN Sensei Super High Efficiency Plus 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 72 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 RUR199iN Sensei Recirculating Tankless Water Heater, and 2 more. The fix may vary by model, so check each model's specific page for tailored repair steps.