Rinnai Rinnai V65iN Value Series Tankless Water Heater 43 Error Fix: Heat Exchanger Issue

Error code 43 on the Rinnai Rinnai V65iN Value Series Tankless Water Heater means: Heat Exchanger Issue. The control board has detected a performance issue with the heat exchanger. This code can indicate several conditions: (1) The heat exchanger is not transferring heat efficiently due to heavy scale buildup on the internal waterside surfaces. (2) The heat exchanger has developed a pinhole leak, allowing water to drip onto the burner or into the combustion chamber. (3) The heat exchanger fin surfaces (external/combustion side) are heavily clogged with soot or debris, reducing heat transfer. For waterside scaling, flush the heat exchanger using a submersible pump and a bucket of white vinegar or commercial descaler solution (circulate for 45-60 minutes). For pinhole leaks, the heat exchanger must be replaced — this is a major repair. For soot buildup on the combustion side, the burner and heat exchanger may need professional cleaning. Error 43 often appears on units that have never been descaled and have been operating in hard water conditions for several years.

The most successful fix is "Replace the Heat Exchanger Due to Pinhole Leak or Severe Damage" (hard difficulty, ~180 minutes). This fix costs nothing. 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 ("Replace the Heat Exchanger Due to Pinhole Leak or Severe Damage") is rated hard difficulty and takes about 180 minutes. Tools needed: T20 Torx screwdriver, Adjustable wrench, Multimeter, Pipe wrench.

DIY cost: $0. Professional repair typically costs $600-$900. 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 43 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.