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• The current owing between the Flame Sensor and Burner is DC micro amp current expressed as: µA (micro Amps). Flame sensing
current can be measured with a DC micro amp test meter, see “Tools Recommended” on Page 3.
SPARK
IGNITER
BURNER
FLAME
BURNER
(MUST BE GROUNDED)
CERAMIC INSULATOR
FLAME SENSOR
METAL CONDUCTOR
CONTROL SYSTEM
APPLIES AC CURRENT
TO FLAME SENSOR
C CURRENT FLOWS FROM THE FLAME
SENSOR TO THE BURNER. THE BURNER
MUST BE GROUNDED FOR CURRENT TO
FLOW. DURING THIS PROCESS THE AC
CURRENT IS “RECTIFIED” AND BECOMES
DC CURRENT. DC MICRO AMP CURRENT
THEN FLOWS BETWEEN THE FLAME SENSOR
MINIMUM FLAME SENSING CURRENT
To prove burner ame during the Ignition Verication state the Control System monitors ame sensing current, the DC micro amp (μA)
current owing through the Flame Sensor. The Control System must sense a minimum amount of current to “prove” ame. The
minimum ame sensing current is 1.0 μA. If ame sensing current does not reach 1.0 µA during ignition or falls below this amount
during a heating cycle the Control System will immediately de-energize the 24 Volt Gas Control Valve.
After 3 failed trials for ignition the Control System will lock out and display Ignition Failure (fault condition) on the UIM. If ame sensing
current drops below 1.0 μA during a heating cycle the Control System will de-energize the 24 Volt Gas Control Valve and enter the
Inter-Purge operating state. After the Inter-Purge operating state the Control System will try for ignition again if a call for heat is still
active. See the Sequence of Operation Flow Chart (page 9).
FLAME SENSING CURRENT TEST
During the heating cycle the ame sensing current is normally greater than 8.0 μA with a clean Flame Sensor. Over time the Flame
Sensor can degrade and this will reduce ame sensing current. With heavier use, more heating cycles/greater load, this will occur more
quickly.
Measuring ame sensing current requires a test meter with a DC micro amp function, see “Tools Recommended” on Page 3. The
meter’s selector is set to DC micro amps. The two test leads from the meter are placed in series with the ame sensing circuit. This can
be done at the spade (male/female) ame sensing wiring connectors. See Figure below.
To measure ame current disable water heating by turning off the Enable/Disable Switch located in the front of the water heater and
connect the test meter following the method shown in Figure below. Enable water heating and ensure a call for heat is active - when the
Control System energizes the 24 Volt Gas Control Valve the meter will measure ame sensing current during normal operation.
Service Notes:
• The most common cause of Ignition Failure lock out is a worn Flame Sensor. The Flame Sensor should be inspected and cleaned
anytime the measured ame sensing current is below 8 µA or the Burner has been removed. Clean the Flame Sensor with ultra
ne steel wool. DO NOT use a coarse abrasive material such as sand paper. Inspect the ceramic insulator on the Flame Sensor for
cracks, replace the Flame Sensor if it is damaged.
• An open ame sensing circuit caused by disconnected or loose connectors can also cause ignition failure. Check all wiring and wiring
connections between the Flame Sensor and the J14 connector on CCB circuit board. See CCB Circuit Board Layout (page 35).
• The Burner not being grounded will cause Ignition Failure. See Electrical Connections – All Models (page 26). Ensure the water
heater and the Burner are properly grounded.
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