ServiceNomad RV · Knowledge
RV Water Heater Relief Valve Leaking
The temperature and pressure relief valve (T&P valve) on your RV water heater is a critical safety device designed to prevent tank rupture by releasing pressure if water gets too hot or tank pressure exceeds safe limits. When this valve drips or sprays water, it's doing its job—but persistent leaking indicates either an overpressure condition, a faulty valve, or thermal expansion issues that need to be addressed.
How the Relief Valve Works
The T&P valve has two functions: it opens if water temperature exceeds 210°F (far above the normal 120-140°F operating range), or if tank pressure exceeds 150 PSI. Both conditions are dangerous—they can cause the water heater to rupture explosively. The valve is spring-loaded and normally closed, but when it senses excessive temperature or pressure, it opens and vents water (and steam) through the discharge pipe. Occasional dripping during heating cycles is normal, especially if you're on city water with high incoming pressure. However, continuous dripping or spraying indicates a problem that needs attention.
Thermal Expansion and City Water Pressure
When you heat water, it expands. In a closed system (like when you're connected to city water with the water pump off), this expansion creates pressure. If your incoming city water pressure is already high (over 60 PSI), adding thermal expansion can push the tank pressure high enough to crack the relief valve open. This is especially common with Suburban water heaters that have smaller tanks (6 gallons). The solution is to install a pressure regulator on your city water inlet to limit incoming pressure to 40-50 PSI, or add a thermal expansion tank between the water heater and the rest of the plumbing system. This gives the expanding water a place to go without building excessive pressure.
Failed or Stuck Relief Valve
Relief valves don't last forever. Over time, mineral deposits, corrosion, or age can cause the valve to fail in either direction: it may stick open and drip constantly even under normal conditions, or it may stick closed and fail to open when needed (a dangerous situation). If the valve is dripping constantly and you've ruled out overpressure, the valve likely needs replacement. Replacement involves draining the water heater, unscrewing the old valve, and installing a new valve with thread sealant (not Teflon tape, which can clog the valve). This is a straightforward repair but requires working with hot water and plumbing connections—many owners prefer to have a technician handle it.
Overheating Thermostat Failures
In rare cases, the water heater thermostat fails in the 'on' position and continues heating water beyond the safe limit. The water gets dangerously hot (approaching boiling), and the relief valve opens to prevent tank rupture. This is a serious malfunction—an overheating water heater can scald anyone who opens a hot water faucet and can cause tank failure. If water coming from the relief valve is extremely hot or steaming, shut off power (electric water heaters) or propane (gas water heaters) immediately and let the tank cool. A technician will need to test and replace the thermostat and possibly the heating element or gas control valve.
⚠️ Safety Notes
- Never plug, cap, or block the relief valve discharge pipe—this can cause the water heater to rupture explosively.
- If the relief valve is venting steam, stay away from the discharge pipe—steam burns are severe.
- Test the relief valve annually by lifting the lever and ensuring water flows freely—a stuck valve is a safety hazard.
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