The Pressure Relief Valve, often called the Temperature and Pressure Relief Valve (T&P Valve), prevents failure in water heaters. This device automatically opens and discharges hot water if the internal pressure exceeds 150 pounds per square inch (psi) or the temperature reaches 210 degrees Fahrenheit. Without this mechanism, pressure created by superheated water could compromise the tank’s integrity, making its function paramount for safety. Replacement is necessary when the valve leaks or drips continuously, indicating mineral deposits have fouled the valve seat, or when the mechanism fails a manual test. A faulty T&P valve must be addressed immediately to manage thermal expansion and pressure fluctuations within the closed water heater tank.
Essential Safety Preparation
Before beginning any work, all energy sources supplying the water heater must be disconnected to eliminate the risk of electric shock or gas ignition. For electric units, switch off the appropriate circuit breaker in the main electrical panel. For gas heaters, turn the gas control valve to the “pilot” or “off” setting. Next, halt the flow of cold water into the tank by closing the cold water inlet valve, typically located above the unit. This isolates the water heater from the household plumbing system.
The tank must then be partially drained to lower the water level below the T&P valve connection point, which is generally located near the top of the tank. Connect a garden hose to the drain valve at the bottom of the heater, running it to a safe drain or outside area. Opening a nearby hot water faucet will introduce air into the system, preventing a vacuum and allowing the water to drain effectively until the level is safely below the valve. You will need a pipe wrench, Teflon tape or a suitable pipe thread sealant, and a replacement T&P valve that matches the specifications stamped on the old unit.
Replacing the Valve Step-by-Step
Once the water level is sufficiently low, disconnect the discharge pipe or drain tube attached to the old valve; this may release a small amount of residual water. Using a pipe wrench, apply firm, counter-clockwise pressure to the hexagonal fitting of the old valve to unscrew it from the tank opening. If the valve is corroded and difficult to loosen, a penetrating oil can be applied to the threads to aid in its removal.
After the old component is removed, the threads on the tank’s port should be cleaned to ensure a proper seal with the new valve. Prepare the threads of the new T&P valve by wrapping them with plumber’s Teflon tape, ensuring the tape is applied in a clockwise direction to prevent unraveling as the valve is tightened. Wrapping the threads three to four times, while leaving the last thread exposed, helps create a watertight connection.
The new valve is then carefully threaded into the port and tightened clockwise using the pipe wrench until it is secure. Do not overtighten, which could damage the threads on the tank or the valve itself. The valve’s outlet must be positioned to point downward before the discharge pipe is reconnected, ensuring any discharge is directed safely towards the floor or a drain.
Recommissioning the Water Heater
With the replacement complete, the drain valve at the bottom of the tank should be closed and the hose removed. The tank can be refilled by slowly opening the cold water inlet valve that was previously shut off. Keep the closest hot water faucet running until a steady, smooth stream of water flows out, which indicates the tank is completely full and air pockets have been purged from the system.
Once the tank is full, check all connections, especially the new valve threads, for any signs of leakage before restoring power or gas. Applying heat to an empty or partially filled tank can lead to damage to the heating elements or tank lining. After confirming the absence of leaks, the energy supply can be restored by flipping the circuit breaker or setting the gas control back to the desired temperature setting. The system should be monitored over the following hours to ensure the new valve remains dry and the water heater operates normally.