Suburban and Atwood tank water heater fault codes
Atwood DSI is a series string: 12V (battery or the filtered side of the converter) → ON/OFF switch inside the coach → thermal cut-off (one-shot fuse, opens at 190°F, e.g. blocked burner or flue) → thermostat (normally closed, opens about 140°F) → circuit board. The board feeds the gas valve through the E.C.O. (normally closed, opens if water exceeds 180°F). Suburban: the thermostat/ECO controls power to the module board; if the thermostat fails the ECO opens and must be manually reset.
RV water heater: Spark, no gas
Gas not getting to the burner. 11 in. W.C. with 2+ appliances running; 10.5 VDC minimum; blocked burner tube or orifice; loose ECO or solenoid wires; dirty edge connector; bad ECO, valve or board.
RV water heater: Gas, no spark
Ignition side. HV lead loose at the board; electrodes loose on the burner; gap not 1/8 in. or out of the flame path; dirty or cracked porcelain; bad board.
RV water heater: Gas and spark, still locks out
Flame not being proven. Gas pressure, low voltage, poor ground, electrodes out of flame or sparking to the burner screw, partial burner/orifice blockage, air shutter about 1/4 open, flame spreader square to the tube.
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Full field guide: Suburban and Atwood tank water heater
Codes come from the maker manuals and public service sheets. Your model's own chart always wins, and LP and 120 volt work belongs to a qualified technician.