Watts 0066090 3/4 IN Brass Self Closing Temperature and Pressure Relief Valve, 125 psi, 210 degree F, Test Lever, 4 IN Ext Thermostat

Yes. The Watts 100XL 0066090 has a 3/4 inch male NPT inlet that threads into a 3/4 inch female tapping on the heater, and a 3/4 inch female NPT outlet for the discharge tube. Shank length under the threads is 1.1875 inches, so the 4 inch copper probe extends past the tank wall into the water.

It relieves at 125 psi or 210 degrees F, whichever comes first. That makes it a match for a water heater with a 125 psi maximum working pressure rating. If your heater is tagged for a lower relief setting, this is the wrong valve for it.

The 0066090 is rated for 105,000 BTU per hour of steam discharge on both the temperature and pressure sides. The relief valve has to be rated at or above the input rating of the heater it protects, so it covers residential and light commercial heaters up to 105,000 BTU/hr input. A larger input heater needs a higher capacity valve.

Yes, match the probe. The 0066090 carries a 4 inch extension thermostat, which is the long-probe version used where the tapping sits in a thick jacket or on tanks specified for an extended element. Swapping a 4 inch probe for a short shank one leaves the sensor out of the water, and vice versa a 4 inch probe may bottom out where a short one was fitted. Also confirm the existing valve was set at 125 psi.

No. It's built for water heater service, with a 210 degree F temperature relief and a 125 psi setting. Hydronic boilers take a separate pressure-only relief valve, typically set at 30 psi, not a 125 psi T&P.

That's the range the 100XL family is offered in. This particular valve, model 66090, is factory set at 125 psi and is not field adjustable. If your job calls for a different setting, order the 100XL built to that setting rather than trying to change this one.

Yes, it comes with a test lever, which is what a maintenance tech or property manager uses to flush the seat once a year and confirm the valve isn't seized. It's a self-closing design, so it reseats after the test or after a relief event.

The valve itself is just the 3/4 inch valve. You supply the discharge piping: a 3/4 inch line off the female NPT outlet run full size, downward, and terminated where it can discharge safely. Nothing may be threaded into or valved off that outlet.

Brass body with a copper extension thermostat probe. Both are standard for potable hot water service and won't be attacked by the water side of a residential heater. The probe is 4 inches long, so it reads tank water temperature rather than the temperature at the tapping.