Rinnai FUA-E, Service Manual, Page: 12 / 67

12
Main Components
1. Gas Control Unit
1.1 Modulating Valve
This device is used by the PCB to adjust the volume of gas to the burner in proportion to the
volumetric flow rate of water in order to maintain a supply of constant temperature hot water
amid changes in water flow rates and incoming temperatures.
1.2 Change-over Solenoid Valves
Additional solenoid valves are included to section the burner and stage the control in 3
steps. This gives the Burner more steady combustion at the required capacity and allows
the water heater to operate at very low flow rates and temperature rises.
2. Flame Rod
Monitors combustion characteristics inside the combustion chamber. If the flame fails, gas
supply is stopped. Works through rectification of the combustion flame. An AC current is
supplied to the flame rod. Electrons can only pass from the rod to the burner, and never
from the burner to the rod, so the resultant DC current is used to prove combustion. When
the DC current is present the burner has normal combustion, if the DC current is not present
(or an AC current is present) the unit shuts the solenoid valve.