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DSI stands for direct spark ignition. DSI means that the water heater can be automatically lighted by a switch inside the RV.
Direct spark ignition was invented by the Fenwal Company. Before DSI, water heaters were turned on by lighting the pilot flame outside the RV.
The light switch activates the burner, which heats the water until it reaches the set temperature. Once this temperature is reached, the burner goes out, restarting only when the heated water is used.
Direct spark ignition is easier and safer than using a pilot flame; the DSI circuit board closes the gas valve automatically as soon as the set temperature is reached.
Make sure there is water in the heating tank before using the water heater for the first time by connecting the RV to a water source, checking to see if the bypass valve is open and turning on the on-board water pump.
Suburban and Atwood are the two largest producers of RV DSI water heaters, most in the six- to 10-gallon range.