Water Heater Pressure Relief Valves: What Homeowners Need to Know

The temperature and pressure relief valve — universally called the T&P valve — is the most critical safety component on your water heater. It is the last line of defense against a scenario that every plumbing code is designed to prevent: a water heater becoming a pressurized vessel that ruptures catastrophically. Here is what homeowners need to know.

What the T&P Valve Does

Your water heater heats water inside a sealed tank. Under normal operation, this is managed safely by the thermostat. But thermostats fail. Gas valves can stick open. If the water temperature rises above 210°F or the pressure exceeds 150 PSI — the typical relief settings — the T&P valve opens automatically, releasing hot water through the discharge pipe to relieve the pressure before the tank fails.

The failure mode the T&P valve prevents — a superheated pressurized tank that ruptures — can cause catastrophic structural damage and serious injury. The T&P valve works. But only if it is functional.

How to Test Your T&P Valve

Testing should be done annually. The procedure takes about 60 seconds:

1. Place a bucket under the T&P valve discharge pipe
2. Lift the valve's lever briefly — 2 to 3 seconds
3. You should hear a rush of hot water or steam and see water flow into the discharge pipe
4. Release the lever — it should seat completely and stop flowing

If no water flows when you lift the lever, the valve has seized and must be replaced. If the valve continues to drip after you release the lever, it is not seating properly and must be replaced.

T&P Valve Discharge Pipe Requirements

The discharge pipe connected to the T&P valve is as important as the valve itself. Code requirements:

• Must terminate within 6 inches of the floor, to a floor drain, or to the exterior of the building
• Must be the same diameter as the T&P valve outlet (typically 3/4 inch)
• Must run downward — no upward loops or traps that could prevent drainage
• Must not be capped, plugged, or reduced in size
• Must not terminate in the crawlspace or attic

When to Replace the T&P Valve

• If it does not open during testing
• If it continues to drip after testing (valve not seating)
• If it shows visible corrosion or mineral deposits on the body
• Every 3–5 years as preventive maintenance, regardless of condition
• Any time the water heater is replaced (a new unit should get a new T&P valve)

T&P valve replacement is included in WaterHeaterMan installations when the existing valve shows signs of age or wear. Every installation is performed per UPC/IPC requirements for valve rating and discharge pipe configuration.