Watts 0342691 30 PSI Pressure Relief Valve, Bronze, 3/4" 335 M2-030

Why I chose this relief valve

I replaced a tired boiler relief valve last heating season after noticing a slow, persistent drip at the discharge line. My hydronic system is conventional: closed-loop, 30 psi design, and 3/4-inch safety relief tapping. I wanted a straightforward, bronze-bodied valve without extras—a part that would thread in, hold tight, and open at the correct set pressure. The Watts valve checked the boxes: 30 psi set pressure, 3/4-inch connections, and a generous 510,000 BTU rating that easily exceeds the input of most residential and light commercial boilers.

Beyond specs, I liked that it’s a no-frills, serviceable design. Relief valves aren’t a place for gimmicks; they’re a place for predictable operation and clean reseating. That’s exactly what I’ve seen in use.

Build quality and design

The body is bronze, with clean machining on the threads and a positive-feeling test lever. The spring action feels stout but not sticky—when you work the lever during maintenance, it opens decisively and snaps back cleanly. The bonnet and lever components are robust; nothing about it feels flimsy or like it would loosen up with normal handling.

The valve I installed is female 3/4-inch on both inlet and outlet. This meant I used a short brass nipple to mate it to my boiler’s tapping and then attached a full-size discharge tube to the outlet. The form factor is compact enough to fit in tight boiler jackets, though you’ll still want to check lever clearance against flue pipes, cabinet panels, or nearby air separators. The outlet is oriented for a straight run of discharge piping down to a floor drain, which keeps installation tidy.

Installation and setup

I swapped the valve as part of a routine service call, and the process was straightforward:

1. Shut down power and fuel, let the boiler cool, and isolate the system.
2. Drain the system to drop the water level below the relief valve tapping, and bleed pressure to zero.
3. Remove the old valve with a backup wrench on the boiler fitting to avoid twisting the casting.
4. Prep the threads. I used PTFE thread tape on the male nipple—enough wraps to seal without bunching. You can use tape or a compatible pipe sealant, but keep it off the first couple threads so you don’t push debris into the valve body.
5. Thread in the nipple, then the valve, ensuring the valve is installed vertically with the spring chamber upright and the outlet pointing down.
6. Install a full-size (3/4-inch), unobstructed discharge line to a safe, visible termination (no valves, no reductions), typically within a few inches of the floor or over a floor drain.
7. Refill, purge air, and bring the system back online. I then watched for leaks and checked the boiler gauge as the system warmed.

Everything sealed on the first try with tape alone. No weeping at the threads and, more importantly, no “seat chatter” or post-cycle drips from the valve itself.

Performance under normal operation

Under normal heating cycles, my system tops out around 20–22 psi at temperature. The valve stayed quiet and dry through repeated firing cycles. I look for two things with a relief valve: it shouldn’t be a chronic weeper, and if it ever has to lift, it should reseat and stay sealed.

During annual maintenance I did a controlled lift using the test lever after confirming clean water and a clear discharge line. The valve opened promptly with a firm pull, discharged cleanly, and then reseated without any persistent drip. That smooth reseat is what separates a valve you forget about for years from one that becomes a nuisance a week after installation.

A note from experience: if your hydronic water is dirty—rust, magnetite, or other debris—it’s easy for grit to lodge on the seat after a lift. If you think your water quality is questionable, flush the system or the valve outlet before testing with the lever. I also like to check the expansion tank precharge and condition at the same time; a failed expansion tank is a common culprit behind frequent relief valve openings.

Sizing and compatibility

This valve is set to 30 psi and has a 3/4-inch inlet and outlet, making it suitable for standard hot-water (hydronic) boiler systems—not steam. The 510,000 BTU capacity is more than enough for the vast majority of residential boilers and many light commercial units. When sizing, make sure:

• The set pressure (30 psi) matches your boiler’s design and nameplate.
• The connection size (3/4-inch) matches the boiler tapping.
• The relief capacity (BTU rating) is equal to or greater than your boiler’s input rating.

In my case, pairing this valve with a ~120,000 BTU boiler was a non-issue. If your boiler’s input is higher, confirm the capacity—this model’s rating gives plenty of margin.

Day-to-day reliability

I installed the valve mid-season and ran it through a full heating cycle as well as shoulder-season operation. It’s stayed bone dry with no intermittent weeping. Pressure readings have been consistent, and it hasn’t chattered or lifted unexpectedly. That’s how a relief valve should behave: invisible until you need it, and drama-free afterward.

It’s also held up well physically. The lever action remains crisp, and the finish hasn’t oxidized beyond the normal bronze patina. I don’t expect to touch it again until the next annual service.

Safety and best practices

A few practical reminders from the field:

• Install vertically with the discharge pointed down.
• Use a full-size discharge tube, no valves or restrictions, and terminate in a visible, safe location.
• Don’t reduce the discharge size; keep it 3/4-inch all the way.
• Keep sealants out of the valve inlet threads to avoid fouling the seat.
• If you manually test the lever, do it during maintenance, and only when you’re prepared to flush out any debris. Avoid “just to see” tests in the middle of the season.
• If the valve lifts, investigate root causes: expansion tank issues, overfilling, a failed pressure reducing valve, or an overheated boiler.

What I liked

• Simple, reliable operation with a clean reseat
• Bronze construction and good machining on threads
• Generous 510,000 BTU capacity for broad compatibility
• 3/4-inch connections that match common boiler tappings
• Easy installation and no fuss sealing with PTFE tape

What could be better

• The test lever can be a knuckle-scraper in tight compartments; plan your clearances.
• Female inlet means you’ll likely need a short nipple; not a problem, but one more fitting to have on hand.
• As with any relief valve, dirty system water can cause post-lift weeping—address water quality before testing.

Who it’s for

If you’re maintaining a standard closed-loop hot water heating system that calls for a 30 psi safety relief, this is a sensible, right-sized option. It’s well suited for homeowners comfortable with basic hydronic maintenance and pros who need a reliable, off-the-shelf replacement. It’s not for steam boilers or systems requiring a different set pressure.

Recommendation

I recommend this Watts relief valve. It’s a straightforward, well-built part that installs easily, opens at the right pressure, and—most importantly—reseats without nagging drips. The 510,000 BTU rating covers a wide range of boilers, and the 3/4-inch connections make for a clean, code-compliant installation with standard fittings. If you match the set pressure and capacity to your boiler, pipe the discharge correctly, and keep up with system maintenance, this valve should provide years of quiet, dependable service.