Tank water heater: suburban + atwood dsi
How the 12V gas side is wired
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.
Sequence
Suburban DSI: board delays 5-7 seconds, then opens the gas valve and sparks at the same time. No flame in 6 seconds = stop. It tries again (3-try systems have a 15 second purge before each spark cycle) then locks out and lights the lockout light. The light can also come on for about 15-18 seconds at startup and during purge. Some DSI boards are single-try.
Atwood DSI: for 6-8 seconds the board sends voltage to the gas solenoid valve and the electrodes. No flame sensed = lockout and the non-ignition light at the ON/OFF switch comes on.
Reset
Suburban: switch OFF for about 10 seconds, then ON. (Owner instructions say wait 5 seconds.) First start after a tank change may take several cycles to purge air.
Atwood: switch OFF and back ON.
Suburban: no burner at all? Switch off, LP empty/off, or the ECO reset button tripped.
Atwood lockout chart
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.
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.
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.
Specs
DC VOLTAGE|10.5 to 13.5 VDC (Suburban); 10.5 VDC minimum to open the Atwood valve
GAS PRESSURE|11 in. W.C. to the control (Atwood: set with two gas appliances running)
ELECTRODE GAP|1/8 in., in the flame path
THERMOSTAT / ECO / TCO|Atwood: stat ~140°F, ECO 180°F, thermal cut-off 190°F (one-shot)
SUBURBAN ELEMENT|120 VAC, 1440 W, 12 A, about 10 ohms
RELIEF VALVE (ATWOOD)|125/150 psi, 210°F
Tank protection
Suburban steel tanks have an anode rod on the drain plug. Replace it when more than 75% is consumed. Running without the anode voids Suburban's tank warranty. Pull it (store it) if you winterize with antifreeze.
Atwood tanks are clad aluminum (7072 alloy lining) and do not use an anode. Flush regularly instead. Rotten-egg smell: follow Atwood's flushing procedure.
Never turn on the 120V element with the tank empty. The most common electric-side failure is energizing the heater before it is full of water.
SUBURBAN|Suburban Water Heater Service Manual: DSI sequence, reset, anode, element data (via myrvworks.com, OCR)
ATWOOD|Atwood Water Heater Service Manual: DSI sequence, lockout chart, clad tank, relief valve (via myrvworks.com)