Rinnai ENERGYSAVER RHFE-308FTR Service Manual page 21

10. Overheat Control Method
The overheat thermistor activates the overheat sensor and the filter indicator, as well as increasing the fan
rpm.
(A) Overheat Sensor
The overheat thermistor activates at different temperatures for different gas rates (combustion).
(B) Filter Indicator
Note 1: Once the overheat limit temperature has been sensed and the filter indicator begins flashing, it
will not go out, even if the temperature falls below the limit.
Note 2: Once the filter indicator begins flashing, gas input is limited to roughly 88% of high combustion.
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