A.O. Smith GAHH 40 100 ユーザーズマニュアル

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The figure below shows the water heater’s sequence of operation when a call for heat is initiated. The gas 

control valve/thermostat will attempt to light the burner three times. If the flame sense rod in the burner/

manifold assembly does not detect ignition, the control will enter lockout mode indicated by the electronic 

control display’s flashing of the appropriate status code.

Main burner flame is detected by 

flame sense rod. Air intake fan 

and main burner will continue to 

operate until water temperature 

inside the tank reaches 

temperature set point.

Gas valve/thermostat will do a 

relay check (relay clicks will be 

heard).

Display will show temperature 

set point during call for heat.

System will verify pressure 

switch operation and start a 

5 second pre-purge, then air 

intake fan will turn off.

Ignitor will start a 12 second 

warm up period. “IGN” will 

show on display.

Gas valve/thermostat will open 

for 4 second trial for ignition 

and fan will turn on.

Gas valve/thermostat is de- 

energized and air intake fan 

continues for a post purge time 

of approximately 5 seconds.

Water heater returns to standby 

mode.

Call for heat indicated by 

flashing of display screen 

status codes.

Draft Blower is energized.