Rinnai Rinnai RSC160iN Condensing Combi Boiler 16 Error Fix: Over Temperature

Error code 16 on the Rinnai Rinnai RSC160iN Condensing Combi Boiler means: Over Temperature. The outgoing water temperature has exceeded the maximum safe limit. The outlet thermistor is reading a temperature higher than the set temperature plus the allowable overshoot (typically above 185°F / 85°C). The unit shuts down immediately to prevent scalding. Causes: (1) Low water flow rate — a partially closed valve, clogged filter, or sediment in the water lines reduces flow, allowing the small volume of water passing through the heat exchanger to overheat. Check and open all isolation valves fully. Clean any inlet water filters. (2) Scale buildup in the heat exchanger — mineral deposits reduce the internal diameter of the heat exchanger tubes, restricting flow and causing localized overheating. Flush the heat exchanger. (3) Stuck bypass servo valve — the bypass valve mixes cold incoming water with heated water to achieve the set temperature. If stuck, inadequate mixing occurs. (4) Faulty outlet thermistor — if the sensor is miscalibrated or reading low, the unit continues to heat past the true set temperature. Check thermistor resistance values against the service manual chart. Error 16 is self-resetting — once the water temperature drops to a safe level, the unit can be restarted.

The most successful fix is "Flush Heat Exchanger and Test/Replace Outlet Thermistor" (medium difficulty, ~60 minutes). Estimated DIY cost: $5-$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 ("Flush Heat Exchanger and Test/Replace Outlet Thermistor") is rated medium difficulty and takes about 60 minutes. Tools needed: T20 Torx screwdriver, Multimeter, Adjustable wrench, Garden hose.

DIY cost: $5-$20. Professional repair typically costs $120-$180. Many homeowners save money by trying the top-ranked community fix first.

The Rinnai Rinnai RSC160iN Condensing Combi Boiler 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 16 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 RU130iN Sensei Super High Efficiency Plus Tankless Water Heater, Rinnai RU199iN 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.