Phase 3 Water Heater Troubleshooting
The Short Answer: “Phase 3” is Suburban’s DSI (direct spark ignition) RV water-heater platform — SW6DE, SW10DE, SW16DE and related. It clicks, sparks, and either lights or lockouts. No standing pilot. Failures are empty tank/ECO, dead board, cracked igniter, or LP supply. Hear spark with the gas off before you buy a board. For the 10-gallon electric half, see SW10DE.
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Search Intent & The Real Problem
The interior switch is on. You hear a tick-tick at the exterior door, then silence. Or you hear nothing. Phase 3 replaced standing-pilot Suburbans; people still hunt for a pilot orifice. There isn’t one. The board runs a spark trial, proves flame on the sense electrode, then holds the gas valve. No proof = lockout.
What other guides get wrong
They paste residential-tank pilot steps onto Phase 3. They also call every Suburban a “Dometic.” Atwood/Dometic DSI boards are not Suburban Phase 3 boards. Wrong board, wrong connector, melted harness.
Step-by-Step Troubleshooting
Step 1: Confirm Phase 3 and a full tank
- What to look for: “Phase 3” on the door or board. Bypass valves in normal. Water at a hot faucet without sputtering. Electric switch off while you diagnose gas so you do not dry-fire the element.
- Required tools: Flashlight, cabinet diagram.
Step 2: Listen before you buy parts
| Sound | Meaning | Next |
|---|---|---|
| No click at all | Switch, fuse, board power, or ECO open | 12V at board, ECO |
| Click, no spark | Igniter wire, cracked ceramic, board | Spark test, gas off |
| Spark, no light | LP off, regulator, solenoid, air in line | Bottles, then tech |
| Lights, then dies | Flame sense, dirty electrode, ECO | Clean electrode; don’t keep cycling |
| Rapid click forever | Board or sense wire | Licensed/RV tech |
- Required tools: Your ears at the exterior door.
Step 3: Spark test with fuel off
- What to look for: LP bottles closed. Switch on. A sharp spark at the electrode gap (about a business-card gap — do not bend it into a pretzel). No spark at the tip but board clicks = wire or ceramic. No click = power or board.
- Required tools: Eyes, gas off. No screwdriver across the electrode on a live board.
Step 4: ECO and 12-volt power
- What to look for: ECO/thermal cutoff on the tank jacket. A dry-fired or overheated Phase 3 will be electrically dead until it cools and the ECO is reset or replaced. Coach 12V low (under ~10.5 V) makes boards act possessed.
- Required tools: Meter on the board’s 12V supply if you are qualified.
Step 5: LP supply — still not a DIY purge
- What to look for: Bottles open, pigtail not stripped, regulator icing, other LP appliances lighting. If the furnace lights and the water heater does not, the problem is at the heater. If nothing LP lights, fix supply first.
- Required tools: None on the fittings. Smell = stop.
Air in an LP line after a bottle swap can delay ignition. That is still not a reason to loosen flare nuts. See gas line air.
When DIY Ends: Calling a Licensed Pro
Stop at gas-valve/solenoid replacement, board diagnosis beyond a visual fuse, LP leaks, and any burner-box that smelled of gas. You may fill the tank, confirm bypass, hear spark with fuel off, and reset a cool ECO once. Phase 3 boards and igniters are RV-tech parts. A cracked tank or a burner full of spider nests after storage is a clean-and-inspect, not a second Amazon board.
Frequently Asked Questions
Q: What is a Phase 3 water heater? A: Suburban’s DSI RV water heater — spark ignition, no standing pilot — used on SW-series 6, 10, and 16 gallon units with an electronic board.
Q: Why does my Phase 3 water heater click but not light? A: Spark with no fuel, or fuel with a gap that will not ignite. Confirm LP bottles and spark with the gas off. Repeating click-no-light cycles is a fire hazard; hire an RV tech.
Q: Can I replace a Phase 3 board myself? A: If you can prove 12V, match the exact Suburban part, and keep LP off until connections are correct, some owners do. If you smell gas or the harness is heat-damaged, do not. A mobile RV tech is cheaper than a coach fire.