ServiceNomad RV · Knowledge
Suburban Water Heater Relief Valve Dripping
Relief valves on Suburban water heaters are critical safety devices designed to release pressure if it builds up excessively inside the tank. Occasional dripping from the relief valve during heating cycles is normal and expected—it's the valve doing its job. However, constant dripping, heavy discharge, or valve activation when the water heater isn't even running can indicate problems with thermal expansion, pressure regulation, or the valve itself. Understanding when dripping is normal versus problematic helps you determine whether you need service.
Why Relief Valves Drip During Heating
When you heat water, it expands. In a closed system (like an RV water system with the water pump off and no pressure relief), this expansion increases pressure inside the tank. The temperature/pressure (T&P) relief valve is designed to open at a specific pressure (typically 150 PSI) or temperature (typically 210°F) to release this pressure and prevent the tank from rupturing. A small amount of dripping during heating is normal—it's the valve releasing expansion pressure. This is especially common if your city water pressure is high (over 60 PSI), or if your water pump produces high pressure. Some RVs lack a thermal expansion tank or pressure regulator, so all expansion pressure is released through the T&P valve. If the valve drips a few ounces during a heat-up cycle and then stops, that's normal operation.
Constant Dripping or Heavy Discharge
If the relief valve drips constantly (even when the heater isn't running) or releases large amounts of water, it indicates a problem. Possible causes include a failed relief valve (stuck partially open or damaged seating surface), excessive incoming water pressure, or a tank that's developing excessive pressure due to overheating or control failure. A technician will test the valve by manually lifting the lever—it should release water freely and then stop completely when released. If it continues to drip after manual testing, the valve needs replacement. They'll also test incoming water pressure with a gauge—if pressure exceeds 80 PSI, a pressure regulator is needed. Relief valves should be replaced every 3-5 years as preventive maintenance, as they can fail from mineral buildup or corrosion.
Overheating and Thermostat Failure
If the water heater is overheating (producing scalding hot water), the relief valve will activate to release pressure from the superheated water. This indicates a failed thermostat or control that's allowing the heating element or burner to run continuously. Overheating is dangerous and can cause serious burns, tank damage, or even tank rupture if the relief valve fails. A technician will test the thermostat operation, verify the high-limit switch is functioning, and check that the heating element (electric) or burner (gas) is cycling off at the correct temperature. They'll also test the relief valve's temperature rating by checking at what temperature it opens. If the control system is allowing overheating, repair is urgent—do not use the water heater until it's fixed.
Installation and Maintenance Best Practices
Relief valves must be installed with the discharge tube pointing downward and terminating near the ground (typically extending through the floor of the RV or exiting near the wheels). This ensures hot water and steam are safely directed away from occupants if the valve activates under full pressure. The tube should not be capped or plugged—it must be open to allow free discharge. A technician will verify proper installation, inspect the discharge tube for blockages or damage, and exercise the valve annually by lifting the lever to ensure it operates freely. Mineral deposits can cause valves to stick, so periodic testing and replacement is important. Installing a thermal expansion tank (if space allows) can reduce relief valve activation and extend valve life.
⚠️ Safety Notes
- If the relief valve is releasing large amounts of water or steam, shut down the water heater immediately—this indicates dangerous overheating.
- Never cap or plug the relief valve discharge tube—this defeats the safety function and can cause tank rupture.
💡 Prevention Tips
- Replace the relief valve every 3-5 years as preventive maintenance to ensure reliable operation.
- Install a water pressure regulator if your city water pressure exceeds 60 PSI to reduce stress on the relief valve and plumbing.
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