Watts LF40XL-150210 1 1 IN Lead Free Brass Automatic Reseating T and P Relief Valve, 150 psi, 210 degree F, Test Lever, 5 IN Extension Thermostat

Inlet is 1 inch male NPT, outlet is 1 inch female NPT. So it threads into a 1 inch female tapping on the water heater or tank, and the discharge line screws into the outlet. Keep the drain line the full 1 inch and run it downward to an approved termination.

It relieves at 150 psi and at 210 degrees F. Those are the two independent trip points, pressure or temperature, whichever hits first. Confirm the 150 psi setting matches the tank's rated working pressure before you install it, since the valve setting must not exceed the vessel rating.

The LF40XL-150210 uses a lead free bronze body and is flagged lead free, which is what a potable hot water installation needs. It is also listed as Buy American Act compliant, USA, which matters on government, school and healthcare jobs with domestic sourcing requirements.

This one carries a 5 inch extension thermostat with a 4 inch probe, which is built for heaters and tanks with thick insulation or a deep tapping, where a standard short probe would never reach the water. On a thin-wall tank with a flush tapping the long probe can bottom out or sit too far into the vessel, so measure from the face of the tapping to the tank wall before you order.

Rated at 2,134,000 BTU per hour pressure steam discharge and 500,000 BTU per hour temperature steam discharge. The temperature figure is the one that governs sizing on a water heater: the valve's temperature rating must equal or exceed the heater's input, so this covers units up to 500,000 BTU/hr input. Above that you need a larger relief valve.

No. The maximum working pressure is 113 psi and the valve relieves at 150 psi, so the system has to operate below the relief setting or the valve will weep continuously. If your static street pressure is climbing past that, the fix is a pressure reducing valve and an expansion tank, not a higher-set relief.

Order it as Watts LF40XL-150210 1, series LF40L, Watts part number 556008. The suffix reads directly: 150 is the psi setting, 210 is the temperature setting in degrees F, and the trailing 1 is the 1 inch size. Watts builds this family in other pressure settings, so the -150210 portion is what you match.

After the valve relieves and the pressure or temperature drops back into range, it closes on its own rather than staying open and dumping the tank. The test lever lets you manually lift the disc to verify it still moves freely, which is the annual check most maintenance programs require on a T and P.

The thermostat element is copper. That is standard for potable hot water service and pairs with the lead free bronze body, so you are not introducing a dissimilar metal issue at the tapping on a copper-piped system.