Rinnai Continuum REU2532-W Series, Service Manual

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REU-2532W Series 25 Rinnai
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.
1. The fan speed is constantly correcting to provide optimum combustion conditions.
2. To determine the opening degree of the modulating gas valve, so that the gas rate always matches the volume
of air for combustion, as well as the input required to heat the water.
The reason for controlling the opening degree of the modulating gas valve based upon data from the combustion
fan is that, the gas valve is able to react much more quickly to a change in control signal than the combustion fan
is. Controlling the gas valve based upon data from the combustion fan means that combustion remains
satisfactory, even if there are sudden changes in input conditions.
1. 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.
REU-2532 units have an automatic water flow control device.