Rinnai Air Thermistor for 26iV / HD50i - (P26IV-KITH) The air thermistor on a Rinnai 26iV or HD50i continuous flow water heater monitors combustion air temperature, feeding that reading to the control board so it can manage combustion settings correctly. Accurate readings here matter for both safe operation and efficient performance — if the sensor drifts or fails, the control board is working from bad data. A faulty air thermistor typically shows up as incorrect combustion settings, erratic temperature behaviour, or confusing fault codes that don't point clearly to the actual cause. This genuine Rinnai replacement, made to the original specification, restores accurate air temperature monitoring and lets the control board manage combustion the way it was designed to. ⚠ Important: This is an internal component of a gas-fir