Why is my PRV leaking from the adjustment screw?

A PRV is a spring-loaded valve. EPA WaterSense describes the most common kind, the direct-acting valve, as "a globe-type body with a spring-loaded, heat-resistant diaphragm connected to the outlet of the valve that acts upon a spring." The adjustment screw on top sets how hard that spring pushes. Turn it in and the spring pushes harder, so the valve holds a higher pressure. Turn it out and the setting drops.

The spring cage sits above the diaphragm. Watts' service steps for its LFN250 valve begin with "Remove spring cage and all parts above diaphragm." Everything above the diaphragm is the dry side. Water isn't supposed to be up there, so when you see it at the screw, it has come past a seal.

Zurn Wilkins reaches the same place for its Model 600XL. Its inspection instructions say "If there is any leakage observed from the bell, the valve should be repaired." The bell is the housing the adjustment bolt threads into.

So the honest reading of a leak at the adjustment screw is that the valve's internals need attention. The exact part, a diaphragm, a seal ring or an o-ring, depends on the model.

Before you decide the valve is done, check three things.

1. 1Is it really water from the valve? A cold pipe in a humid space can sweat and drip onto whatever is below it. Wipe the valve and pipe dry, then watch for 15 to 30 minutes. Condensation forms a film over a wide area and comes and goes with humidity. A leak comes from one spot and keeps coming. Our page on why pipes sweat in summer shows how to tell them apart.
2. 2Has the screw been adjusted lately? Zurn's instructions say to "Tighten locknut when desired pressure is achieved and test valve to confirm proper operation." A locknut that was never snugged down after an adjustment is worth a look. If the weeping stops after you snug it, keep an eye on it for a few days.
3. 3Is the water coming from the valve body or the bell? Zurn draws a line between the two: "If there is any external leakage from the body the valve should be replaced. If there is any leakage observed from the bell, the valve should be repaired." A leak at the body joint is a different problem than a leak at the screw.

If none of those explains it, the seal has failed.

### Test the pressure

A leaking PRV is often a PRV that isn't holding pressure well either, so take a reading. Screw a hose bib gauge onto an outdoor faucet near where the water enters, turn everything off, and open the faucet fully. Note the number.

Zurn's test is simple. With a gauge on the outlet, open a downstream faucet, close it, then "Observe the gauge for 10 minutes." If the pressure holds, the seat is sealing. If it "slowly creeps up within 10 minutes the valve may be fouled and should be cleaned and retested." A leak at the screw combined with pressure that climbs above your setting points to a valve that's on its way out.

Keep the numbers in perspective. The plumbing code caps the pressure in the building's piping at 80 psi static, and EPA WaterSense recommends incoming pressure "between 45 and 60 psi." Our page on what your home water pressure should be gives the full picture.

A small weep isn't a flood. But a failing PRV can turn into a high-pressure problem, and the code is built around that. IPC 604.8.1 says "The pressure-reducing valve shall be designed to remain open to permit uninterrupted water flow in case of valve failure." That is a safety choice so you don't lose water. The trade-off is that a dead PRV can let full street pressure into your house.

EPA WaterSense says high pressure "can damage plumbing piping, fixtures, and appliances, and can lead to increased water consumption, premature equipment failure, and risk of leaks." So the valve that's dripping at the screw may also be letting through more pressure than your fixtures and hoses were built for. If you hear banging pipes or your water heater's relief valve starts to drip, see why pipes bang and why the relief valve leaks. If pressure jumped, why water pressure suddenly gets too high walks through the checks. The full list of failure symptoms is in the signs a pressure reducing valve is going bad.

Zurn's criteria give a clean way to think about it:

• Damage to internal parts. "If there is any visible damage to the diaphragm, seal ring, stem or stem o-ring, the valve should be repaired." Repair kits exist for many models, and Watts' LFN250 sheet lists a replacement assembly that includes the diaphragm.
• Damage to the body. "If there is any visible damage or corrosion to the bronze body or seat, the valve should be replaced."

Ask the plumber what shape the body and seat are in once the valve is opened up, because that decides which of the two you're in. Zurn also warns that "unauthorized adjustments or repair could render the product ineffective" and says "a qualified licensed plumber must be contacted" if the owner isn't qualified to do the maintenance.

Whatever you choose, the new or rebuilt valve has to meet the code: an approved valve "with strainer," set so pressure to the building doesn't exceed 80 psi static, and installed so it can be repaired without breaking a pipeline. If you have a tank water heater, a replacement is the time to check the expansion tank too, since the PRV keeps the system closed. See do I need an expansion tank.

In Phoenix, the private regulator is yours. The city says "Private pressure regulators are the responsibility of the homeowner." That means the city won't fix it, and it's on you to keep it working.

If the valve is only weeping, dry it and mark the spot so you can tell whether it's getting worse, and get a pressure reading. If it's spraying or the pressure reads high, close the main shutoff and call. HQ Plumbing & Air can test your pressure and replace a failed PRV. HQ is licensed and insured and gives free estimates, with the price up front before work starts. If a leak can't wait, we're available 24/7.

Keep notes for the plumber: when you first saw the water, whether it comes and goes, the static pressure reading, and the valve's model from its nameplate. Zurn's notice says periodic inspection is required "at least once per year or more as service conditions warrant," so a valve that has never been looked at is a fair candidate for a checkup even after this leak is sorted out.

That's the plan. Dry it, test it, and if the seal is going, fix the valve before the pressure does the damage for you.