A.O. Smith 100 Series, Руководство по обслуживанию

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Servicing should only be performed by a Qualified Service Agent
FLAME SENSOR
Ignition of the burner is controlled electronically. The principle of operation for electronic ignition relies on flame sensing voltage to
prove the fuel gas flowing to the burner has been ignited and is burning safely.
Flame sensing requires correct power supply polarity and an adequate earth ground to the boiler/water heater's burner. See Figure
7 on Page 15, Figure 8 and Figure 9 on Page 16 for the Burner Assembly.
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 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 voltage flows from the Flame Sensor through the burner flame to the (grounded) Burner, the AC voltage is "rectified"
and becomes a DC voltage.
• Flame sensing voltage can be measured with a Digital Multi Meter. See Tools Required on Page 4.
Flame Signal Processing
The flame signal processing will monitor the flame sensor. The flame signal voltage at the test jacks or on the bar graph on the display
is the measured voltage in the range from 0V to 30V. The display could show stronger numerical data.
The incoming flame signals are filtered to eliminate transient and spurious events. The flame failure response time (FFRT) is 4
seconds. Flame sensitivity is set by the Flame Threshold parameter, which will provide the ON/OFF threshold specified in volts.
Service Notes:
• Ensure you have identified the correct Flame Sensor wire before performing a flame sensing test to prevent damage to the test
meter.
• The most common cause of ignition failure 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 voltaget is at a minimum
of 1 volt 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 for cleaning. 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.
• An open flame sensing circuit caused by disconnected or loose connectors can also cause ignition failure. Check all wiring
connections between the Flame Sensor and the J1 connector on Control Board.
• The burner not being grounded will cause ignition failure. Ensure the boiler/water heater and the burner are properly grounded.
FIGURE 10. FLAME SENSOR