ServiceNomad RV · Knowledge
Suburban Water Heater Won't Stay Lit
Suburban water heaters are simple and reliable, but when the pilot or main burner won't stay lit, it's one of the most frustrating issues for RV owners. The water heater may light initially, run for a few seconds or minutes, and then shut off unexpectedly. This behavior almost always points to flame sensor issues, airflow problems, or gas supply inconsistencies.
Thermocouple and Flame Sensor Function
Suburban water heaters use a thermocouple or flame sensor to prove that a flame is present before allowing the gas valve to stay open. The thermocouple is a metal probe positioned in the pilot or main burner flame. When heated, it generates a small voltage (millivolts) that holds the gas valve open. If the flame goes out or the thermocouple cools down, voltage drops, and the gas valve closes as a safety measure. A thermocouple that is dirty, corroded, bent out of position, or simply old and weak will fail to generate sufficient voltage. The result: the burner lights, the thermocouple starts to heat up, but before it reaches full operating voltage, the flame is cut off and the process repeats.
Thermocouple Cleaning and Positioning
Over years of operation, thermocouples develop a coating of soot, carbon, and oxidation that insulates them from the flame. Even a thin layer can reduce heat transfer enough to prevent proper operation. Cleaning the thermocouple with fine steel wool or emery cloth often restores function. The thermocouple must also be properly positioned so the flame directly engulfs the sensing tip. If the pilot flame is weak, misaligned, or the thermocouple has been bumped out of position during maintenance, it won't heat adequately. A technician will adjust the pilot flame to ensure it's blue, steady, and envelops the thermocouple tip.
Gas Control Valve and Safety Shutoff
The gas control valve itself can fail internally, causing the water heater to shut down even when the thermocouple is functioning correctly. The valve contains magnets, diaphragms, and internal safety switches that can wear out or become contaminated. If the valve is intermittently sticking or has weak magnetic coils, it may not reliably hold open. A technician can test the thermocouple output voltage (should be 20-30 millivolts or higher when heated) and verify the gas valve is receiving this signal. If voltage is good but the valve still doesn't stay open, the valve needs replacement. Gas control valves are specific to Suburban models and must be matched correctly.
Airflow and Combustion Quality
If the combustion air intake or exhaust flue is restricted, the flame will be starved for oxygen, burn yellow or lazy, and may self-extinguish or produce enough carbon monoxide to trigger safety shutoffs. Insect nests, debris, or ice can block the intake screen or chimney. Even a partially blocked flue can cause rollout or improper draft, leading to erratic flame behavior. A technician will inspect and clean the burner tube, air intake, and exhaust flue. They'll verify the flame is burning blue (indicating proper air/fuel mixture) and that there's no flame rollout or soot buildup in the combustion chamber.
⚠️ Safety Notes
- Never attempt to bypass the thermocouple or manually hold the gas valve open—this defeats critical safety features and can cause gas leaks or explosions.
- If you smell propane or detect gas odors near the water heater, shut off the propane supply and call a technician immediately.
💡 Prevention Tips
- Clean the thermocouple and burner assembly annually to prevent soot buildup and ensure reliable operation.
- Inspect exterior water heater vents for insect nests or debris before each camping season.
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