Blocked Exhaust; Flame Sensor Error - A.O. Smith Cyclone XL 100 Series Service Handbook

4. BLOCKED EXHAUST

B
locked
0 days 0 hrs 0 mins ago
Error Code:
Restriction in exhaust pipe.
Check exhaust pipe and
termination for blockage.
Press the Advanced button for
CHECK/ REPAIR:
• Check pipe for restriction or excessive equivalent length.
• See Instruction Manual for pipe size, length and maximum number of elbows.
• Check actual pipe pressure with a manometer during blower operation..

5. FLAME SENSOR ERROR

F
lame Sensor(error)
0 days 0 hrs 1 mins ago
Error Code:
Flame Sensor rod detected flame
when gas valve should be off.
Shut off gas until repaired.
Call a service professional:
CHECK/ REPAIR:
• Look through sight glass. If flame is present, shut the main gas supply off. See Gas Control Valve section below to confirm proper
operation.
• If flame is not present, cycle the unit Off by turning the Enable/Disable switch to Disable, wait for 5 seconds, and cycle the unit On by
turning the Enable/Disable switch to Enable to see if the error clears.
FLAME SENSOR
Ignition of the Burner is controlled electronically. The principle of operation for electronic ignition relies on flame sensing current to prove
the fuel gas flowing to the Burner has been ignited.
Flame sensing requires an adequate earth ground to the water heater's Burner. See Electrical Connections – All Models (page 26).
FLAME SENSING OPERATION
• The Flame Sensor is a metal (conductor) rod mounted in a ceramic insulator.
• The Control System applies an AC voltage to the Flame Sensor through a single wire.
• The burner flame will conduct a small amount of electrical current.
• The burner must be properly grounded for current to flow from the Flame Sensor to the Burner.
• During ignition the burner flame must make complete and continuous contact with the Flame Sensor.
• As the AC current flows from the Flame Sensor through the burner flame to the (grounded) Burner the AC current is "rectified" and
becomes a DC current.
E
xhaust
A
8-1201
BACK ADVANCED
A B
9-17
BACK ADVANCED
CAUSES:
• The Blocked Exhaust Switch has detected a possible
restriction in the exhaust pipe.
•
CAUSES:
• The Flame Sensor has detected flame when the Gas
Control Valve is supposed to be off.
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