Camco 10421 T&P Relief Valve | 150 PSI 1/2 Inch NPT

A temperature and pressure relief valve isn't glamorous, but it's the one part on your water heater you never want to skip. The Camco 10421 is a T&P safety valve that opens automatically if your tank ever climbs past its safe pressure. It's factory set to relieve at 150 PSI, so the moment internal pressure gets there, the valve vents and protects the tank, the plumbing, and everyone aboard. Think of it as the last line of defense on your hot water system. Small part, big job.

This one uses a 1/2 inch NPT threaded body, which is the standard fitting on the vast majority of RV and marine water heaters. The probe runs 4 inches into the tank, so it reads the actual water temperature and pressure inside, not just what's happening out at the fitting. That probe length is a good match for typical 6 to 10 gallon heaters. If you're working with a compact tank, measure your existing valve first so you know the probe won't bottom out against the far wall.

Where this valve earns its money is the build. The body is corrosion-resistant metal, and the probe is epoxy-coated, so it stands up to the damp, salty air that eats ordinary hardware alive in a bilge or engine bay. And there are no gaskets in the design. That matters, because gaskets are usually the first thing to dry out, crack, and start weeping after a couple of seasons. Fewer failure points means fewer surprise drips under the heater.

Installation is straightforward if you've done any threaded plumbing before. Shut off the water and power, drain enough from the tank to clear the valve port, and thread the new valve in with a few wraps of Teflon tape on the threads. A little anti-seize helps too, especially in a hot engine room where metal can seize up over time. Snug it down, restore pressure, and check for weeping before you call it done. Point the discharge where a release won't spray gear or wiring.

A couple of habits will keep this valve honest. Test it once a year by lifting the lever and letting it snap back, which flushes any mineral buildup off the seat and confirms it reseats cleanly. If your boat runs a closed-loop system, pairing the heater with a small expansion tank keeps normal thermal expansion from nudging the valve open and dribbling every heat cycle. And if your current valve is weeping, seeping, or won't reseat, don't nurse it along. Replace it. A relief valve that won't close is just as much a problem as one that won't open.

So how do you know when a relief valve has gone bad? The usual tells are a steady drip from the discharge, a hiss under normal operating pressure, or a lever that feels stuck when you flip it to test. Any of those, and the valve is done. A little seepage right after a heat cycle can be normal thermal expansion, but a constant drip is not. On a boat that sits for weeks between trips, that slow leak can drain a tank and soak the compartment before you're even back aboard. Catching it early is cheap. Ignoring it is how you end up with a rusted-out heater and a wet locker. When in doubt, swap the valve. It's a few dollars of insurance against a much bigger headache.

One heads-up on the packaging: this ships in bulk, so it comes as the bare valve without a retail box or a printed instruction sheet. That's fine if you know what you're doing, and it keeps the cost down. But if you're installing several across a couple of boats, label them as you go so you don't mix up which tank got the fresh valve. For a standard 1/2 inch NPT water heater, the Camco 10421 is a simple, honest fix you can trust.