Main Components - Rinnai REU-VR1620WG Service Manual

9. Main Components

1) Printed Circuit Board (PCB)
• The Printed Circuit Board controls all operational functions including Air Supply Control, Gas
Control, Water Flow Measurement, Water Flow Control, Combustion System and all sensors and
safety devices.
2) Gas Flow Control
• During normal operation, the PCB keeps the main solenoid valve open whilst there is flow through the
unit and the burner needs to be lit.
• Gas flow rate is controlled by the modulating valve assembly and three changeover solenoid valves to
always ensure constant outlet water temperature, regardless of flow rate or incoming water
temperature.
• The modulating valve is electronically controlled by the PCB using signals from the water flow
sensor, water flow control device, water temperature thermistors and combustion fan speed sensor.
The modulating valve directs gas to the three changeover solenoid valves.
• The changeover solenoid valves direct gas to each of the two burner banks independently. Any one or
two or both of the solenoid valves may be open during operation.
• Gas flow is modulated by a combinationof the modulating valve and changeover solenoid positions.
• The maximum gas rate is predetermined and the appliance cannot be overloaded when correctly
installed.
3) Water Flow Control
• Water flow is detected by a turbine coupled to a magnetic pulse generating device. The magnetic
pulses are detected and counted by the PCB. The PCB calculates the exact water flow from the
frequency of pulses generated by the turbine, as well as the volume of water that has passed through
the unit at any instant during 'Bath fill' operation.
• Water flow control is achieved through the use of servo driven water flow and fixed bypass valves.
(Note: only some models have a bypass valve fitted). Both servo motors are controlled by the PCB.
The 'Water Flow Valve' restricts the flow of water into the heat exchanger assembly if the
programmed temperature cannot be achieved. During normal operation, cold water from the inlet
valve is mixed with hot water from the heat exchanger outlet.
• For models fitted with a 'Bypass' valve, it mixes the correct proportion of cold and hot water to ensure
accurate hot water delivery temperature over the available range of flow rates. The water flow and
bypass valves are a combined assembly on the cold water inlet of the appliance.
4) Air Supply Control
• Air for combustion is supplied by a centrifugal fan driven by a variable speed DC motor. The voltage
to the motor is determined by the PCB based on water flow, delivered water temperature and
programmed water temperature. The actual fan speed is monitored by a magnetic pulse counter. This
counter emits a signal to the PCB. From the voltage supplied to the DC motor and the fan speed
signal, the PCB determines whether an error condition exists with the fan.
5) Combustion System
The combustion chamber is housed within the heat exchanger assembly and comprises:
• A multi chamber aluminium alloy manifold with a multiple integral injectors. Gas flow to each
chamber is controlled by an electronic solenoid valve (refer 'Gas Flow Control' above).
• A burner assembly comprising multiple identical modular stainless steel bunsen burners secured by an
aluminised steel framework. The manifold is attached to the front of the burner module. Each bunsen
burner is supplied by two injectors.
• A combustion chamber. Integrated into the combustion chamber front panel are the flame rod and
ignition electrode(s).
REU-VR1620WG / REU-VR1620WB / REU-VR1620WS / REU-VR2024WG- 14 - Issue 1 - 5/08/09 ©Rinnai