Rinnai B20 Service Manual download pdf (Page 12)

REU-2532W Series 12 Rinnai

7. Safety Devices

Flame Failure

Situated to the right of the burner in the front of the combustion chamber, the flame rod monitors the

combustion process. This sensor monitors the flame intensity, while the PCB compares this signal to the

feed back signal from the combustion fan motor, water flow control, and gas flow through the POV

valve. If any one of the feedback signals are incorrect, the unit will shut off, preventing discharge of

gas to the burner.

Over Heat Protection Device

Also referred to as an Over Heat Switch. This device is fitted to a bend section at the left side of the heat

exchanger. If the flame remains on to the burner after the tap is closed and the water temperature inside

the heat exchanger reaches 194 ° F, a 12 volt DC bi-metal cut-off switch will shut off the gas supply to

the solenoids.

No Water

Should the incoming water flow become restricted or stop, the water flow sensor will cease to send a

magnetic pulse signal to the PCB, in turn preventing gas to flow into the combustion chamber. If you

have restricted flow, first check to ensure the inline water filter is not clogged up.

Thermal Fuse

Wrapped around the entire surface of the heat exchanger you will find a thermal fuse. This device

activates in the event the heat exchanger burns out, or the temperature outside the heat exchanger

reaches 264 °F. If the thermal fuse melts, it breaks an electronic circuit which in turn shuts off the

power supply to the gas solenoids, shutting the unit off.

Combustion Fan Revolution Check

The combustion fan rpm’s are continually monitored by a magnetic pulse generator connected to the

PCB. If the fan revolutions deviate from the speed required for complete combustion, a signal is sent to

the PCB and the revolutions adjust accordingly. (If not the unit shuts down)

Automatic Frost Protection

When the temperature inside the appliance drops below 37 °F , the frost sensing device inside the

appliance activates the anti-frost heaters to prevent the water inside the unit from freezing. The anti-

frost heaters remain ON until the temperature inside the appliance rises to 57 °F. There are five (16) watt

anti-frost heaters located at various points throughout the main water flow area of the appliance. The

unit also incorporates the ability to fire for (3) seconds in the event the anti-frost heaters can not keep

the water temperature from dropping below 37 °F. This unique feature will heat the water in the lines

inside the appliance back up to 57 °F. Both of the above features function as long as the unit has

power and gas. There is an optional freeze protection system that can be added to the unit’s piping. See

the auto drain down drawing in the product Owner’s manual for instructions on how to install the option

freeze protection in the event of a power failure in cold climates.

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Rinnai B20 Service Manual Page 12