Control For Exhaust Temperature (520 Indoor Only) - A.O. Smith Water Heater 520 Direct Vent Indoor Service Manual

CONFIDENTIAL
520 Indoor / 520 Outdoor Service Manual
Ver. 1.00

12-14. Control for exhaust temperature (520 Indoor only)

<Function and Purpose>
The exhaust gas temperature is controlled by the exhaust fan motor.
The 520 Indoor is equipped with a thermistor and hi-limit switch for detecting excess temperatures of
the exhaust gas within the flue and enabling the unit to safely stop operations if needed. These
components are always monitoring exhaust gas conditions in order to prevent heat damage to PVC
(Plastic) venting. If the exhaust gas temperature exceeds 140°F, these components will enable the unit to
safely stop operations. (For the 520 Outdoor model, these components are not available since there's
no exhaust venting required.)
How the safety device works
There is a count that is used for checking the # of events of the exhaust temperature exceeding 140°F
detected by the exhaust thermistor or hi-limit switch for exhaust. If the count reaches 3, the "941"
error code will display and the operation is stopped safety.
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