Watts 0274751 3/4 In Bronze Boiler Pressure Relief Valve, 125 psi, Threaded Female Connections

The 0274751 is factory set to relieve at 125 psi. That is fixed, not field adjustable on your end, so pick the set pressure to match the boiler's maximum allowable working pressure. The 174A family covers set points from 30 to 150 psi, so if 125 psi is above your boiler's rating you need a lower-set version of the same series.

Both ends are 3/4 inch female NPT. Inlet and outlet are the same size, so it threads onto a 3/4 inch male nipple off the boiler tapping and takes a 3/4 inch male-threaded discharge pipe to the drain. No adapters needed if your tapping is already 3/4 NPT.

It is a boiler valve, pressure relief only. The 174A protects against overpressure; it does not include temperature relief, so it is not a substitute for a T and P valve on a domestic water heater. For a water heater you want a combination temperature and pressure relief valve instead.

Rated at 2,070,000 BTU per hour of steam discharge. Size by matching that figure against the boiler's gross output or input rating as required by code: the valve's relieving capacity must equal or exceed the boiler's rating. Anything up to roughly 2 million BTU/hr output is covered by this single 3/4 inch valve.

Usually not the right pick. Most residential hot water boilers are rated 30 psi, and a relief valve must be set at or below the vessel rating, so a 125 psi valve would let pressure climb far past a 30 psi boiler's limit. The 125 psi version suits high pressure commercial or industrial boilers rated at least 125 psi. For a typical residential job, order the 30 psi set point from the same 174A range.

Maximum temperature is 250 degrees F, which covers normal hydronic hot water boiler operation. The body is bronze, so it holds up in closed-loop boiler water service.

Yes, it has a test lever. That lets maintenance staff lift the disc manually to verify the valve is free and flush debris off the seat, which is the routine most boiler maintenance schedules call for. Discharge piping still needs to terminate where a hot water blowdown will not injure anyone.