Bradford White IGI-180R-10 Service Manual page 16

III - MAIN COMPONENTS
(cont.)
5. Combustion Fan
Air for the combustion is supplied by a centrifugal fan
driven by a DC motor. After a pre-purge period of 0.2
seconds, the fan speed is controlled by the PCB to
provide the correct volume of air for combustion. The
calculation for the fan speed is based upon incoming
water temperature, water flow and the temperature
selected on the remote controls.
The actual speed of the motor is continuously monitored
by a magnetic pulse sensor.
This sensor emits (4) pulses per rotation of the fan. This is
the fan feedback or confirmation data processed by the PCB.
The fan speed is constantly correcting to provide optimum combustion conditions. In addition, the
fan speed will determine the opening degree of the modulating gas valve. This enables the gas rate to
always match the volume of air for combustion, as well as the input required to heat the water.
6. Water Flow Sensor and Water Flow Control device
Water flow is detected by a turbine/magnetic pulse generating device. Water flows through the
turbine/magnetic sensor providing information to the PCB by generating a pre-determined number of
pulses in proportion to the water flow. These pulses are counted by the PCB – no pulse indicates no
water flow. The frequency of the magnetic pulses increases as the water flow increases, this enables
the PCB to calculate the exact water flow, and determine the water flow in gallons per minute. As
soon as the required water flow is detected, the PCB activates the combustion fan. The combustion
fan speed is monitored by a magnetic pulse sensor. The output from this sensor is processed by the
PCB which opens the gas modulating valve to a degree proportional to the fan speed. See above for
further details on the combustion fan.
The water flow control consists of a plug and barrel valve which is rotated by a motor to increase or
decrease the volume of water passing through the heat exchanger.
Automatic water flow control device.
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