Flame Sensing Current Test - State Water Heaters 120 Series Service Handbook

flame sensing current test

during the heating cycle the flame sensing current is normally between 8.0 μA and 12.0 μA with a clean
Flame Sensor. over time the Flame Sensor will accumulate corrosion (rust) and this will reduce flame sensing
current. With heavier use, more heating cycles/greater load, corrosion will occur more quickly.
FLAME SENSING TEST BEHIND
THE CCB ENCLOSURE
IGNITER/FLAME SENSOR
WIRING HARNESS FROM CCB
Service Notes:
• The Flame Sensor wire behind the CCB is one of three wires in a harness that also serves the Igniter.
Ensure you have identified the correct wire before performing a flame sensing test to prevent damage to
the test meter. A female spade connector is used at the end of the wring harness from the CCB for the
Flame Sensor, two male connectors are used for the Igniter.
• The most common cause of Ignition Failure lock out is a corroded Flame Sensor. Rust/corrosion
will accumulate on the Flame Sensor over time. The Flame Sensor should be inspected and cleaned
anytime the measured flame sensing current is below 8 µA or the Burner has been removed. Clean
the Flame Sensor with ultra fine 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. The Combustion Blower and Burner must be removed to access the Flame Sensor, see
Combustion Blower and Burner Removal on page 14.
• An open flame sensing circuit caused by disconnected or loose connectors can also cause ignition
failure. Check the spade connector behind the CCB enclosure and check all wiring and wiring
connections between the Flame Sensor and the J4 connector on CCB circuit board, see CCB Circuit
Board Layout on page 41.
• The Burner not being grounded will cause Ignition Failure - see Electrical Requirements on page 6 and
Figure 16 on page 17. Ensure the water heater and the Burner are properly grounded.
Measuring flame sensing current requires a test meter with a dC micro amp
function, see Tools Required on page 2. The meter's selector is set to dC micro
amps. The two test leads from the meter are placed in series with the flame sensing
circuit. This can be done at the spade (male/female) wiring connectors behind the
CCB enclosure or at the J4 spade connection on the CCB circuit board. See Figure
19 below and the CCB Circuit Board Layout on page 41.
To measure flame sensing current turn off power to the water heater and connect
the test meter following one of the two methods shown in Figure 19. Restore power
and ensure a call for heat is active - when the Control System energizes the 24 Volt
Gas Valve the meter will measure flame sensing current during normal operation.
WIRE FROM
FLAME SENSOR
FLAME SENSOR
CERAMIC INSULATOR
Servicing should only be performed by a Qualified Service Agent
FLAME SENSING TEST INSIDE
THE CCB ENCLOSURE
WIRE FROM
FLAME SENSOR
Figure 19
CCB J4 FLAME SENSOR
CONNECTION
19