Rinnai REU-2018W Service Manual page 27

There is no direct connection between the mechanical water flow control device with water flow
sensor and the PCB, therefore, there could be occasions when the input required to heat the
water exceeds the capacity of the appliance, and water at a temperature lower than that
requested on the remote control is output. In this case, manually reducing the water flow at the
tap will increase the temperature.
Once hot water is flowing the water temperature thermistor senses the outgoing water
temperature.
The PCB is continually adjusting both the gas input and water flow to maintain a constant
temperature. It also continually monitors the combustion fan rpm adjusting the gas rate to match.
When the hot water tap is turned off, the water flow sensor stops revolving, and the magnetic
pulse ceases, indicating to the PCB that there is no water flowing, in turn the PCB closes the gas
valves. The combustion fan continues to operate for 65 seconds. This is to provide quicker
ignition when the tap is turned on and off in rapid succession, as it removes the need for a pre-
purge cycle, and allows the burner to re-light immediately when a hot water tap is opened again.
The PCB stores data on the calculated incoming water temperature, ready for when the hot water
is turned on again. The data is used to calculate the initial gas flow.
Infinity REU-2425W - 24 - Issue 2 - 5/07/04 ©Rinnai