REU-VR2626WB (B26) /REU-VR2426WS (S26) /REU-VRM2626WG (INF26) - 15 - Issue 3 - 13/11/14 ©Rinnai
9. Main Components
1) Printed Circuit Board
• 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 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, bypass flow control device (if fitted), water temperature thermistors
and combustion fan speed sensor. The modulating valve directs gas to the changeover solenoid valves.
• The changeover solenoid valves direct gas to each of the burner banks independently. Any of the
solenoid valves may be open during operation.
• Gas flow is modulated by a combination of 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 bypass valves.
(Note: only some models have a by pass 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. Also, when the Bath Fill function is activated, flow of
water is stopped when the bath is full. 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 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 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 multiple injectors, arranged in multiple rows. 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).