A.O. Smith 110 Indoor Service Manual page 43

Error Code
74
Miscommunication between water heater and
temperature remote controller
1 Temperature remote controller (9007666005) or PCB fault
2 Check for signs of power surges.
Error Code
Imperfect combustion
99
(Refer to section 12-3)
1 Check the gas type of the water heater.
2 Check how long the water heater has been installed and in use.
3 Check the installation place.
4 Check the altitude/elevation of area of where the water r heater installed.
5 Check the vent length.
6 Check if there is any blockage in the intake air and/or exhaust.
7 Check if there is dust and lint in burner and heat exchanger, when the water
heater has been installed in laundry room.
8 Check if there is grease and dirt in burner and fan motor, when the water
heater has been installed in restaurant.
9 Check the manifold pressure in the water heater.
Malfunction description
Malfunction description
110 Indoor / 110 Outdoor Service Manual
Restoring
between the water heater and the
Remote controller (9007666005). When
the computer detects proper connections
between the water heater and the
remote controller, "74" error code will
cease to display.
Diagnosis
Turn off the power or water supply
If not possible, press and hold the INC
and DEC buttons on the computer board
simultaneously for more than 3 sec.
Diagnosis
43
CONFIDENTIAL
Ver. 1.01
Cancellation method
proper cable connections
Checkpoint
Cancellation method
Checkpoint