The Rinnai 104000021-K Water Heater Gas Valve Kit regulates gas supply to support proper burner operation in compatible tankless water heaters. It works by adjusting the flow of gas through the valve assembly in response to the heater's operating requirements, supporting the combustion process needed to heat water. Designed for compatible R50, R63LSE2, R75, and R94 models, this replac... https://www.hnkparts.com/104000021-k-rennai-kit-gas-valve-r50r63lse2r75/4-104000021-K.html