Why and When to Drain the Pressure Release Valve
The pressure release valve on a Navien tankless water heater drains by opening a small manual lever or button on the valve body itself, letting trapped water and pressure escape into a bucket or floor drain below. You do this when the system has been sitting unused for weeks, when you're preparing for maintenance, or when you notice water dripping from the valve—a sign that pressure inside the tank has built up beyond the valve's rated limit.
Navien tankless heaters don't store water the way tank models do, but they do hold water in the heat exchanger and supply lines. If that water sits in cold weather or the system cycles on and off without use, pressure can accumulate. Draining the valve releases that pressure safely instead of letting it force water out through the valve seat, which causes the drip.
This is a maintenance task you can do yourself in about five minutes. You do not need to shut off the whole system or drain the entire unit—only the valve itself.
Key Takeaways
- The pressure release valve has a small lever or button on its body that you push or turn to open it and let water drain out.
- Place a bucket underneath the valve opening before you open it, because water will flow out quickly and may be warm.
- Open the valve slowly at first to release pressure gradually, then open it fully until water stops flowing.
- If water continues to drip from the valve after you close it, the valve seat may be stuck and you should contact a technician.
- Draining the valve takes about five minutes and requires no tools other than a bucket and possibly a small flathead screwdriver.
Locate the Pressure Release Valve on Your Navien Unit
On most Navien tankless models, the pressure release valve is mounted on the side or bottom of the unit, near the cold water inlet. It looks like a small cylinder about two inches long, usually brass or stainless steel, with a lever or button sticking out from the body. The lever may be red, black, or silver depending on your model year.
Check your Navien manual or the unit's label to confirm the exact location—some models mount it on the front panel, others on the back near the water connections. If you cannot find it, look for the cold water supply line coming into the unit; the pressure valve is usually within six inches of that connection.
Before you touch anything, make sure the unit has been off for at least 15 minutes so the water inside has cooled slightly. The water in the heat exchanger can stay hot for a while after shutdown.
Set Up Your Workspace and Safety Precautions
Place a bucket or shallow pan directly underneath the valve opening. The opening is usually a small port on the bottom or side of the valve body—water will flow out of it when you open the valve, and it may be warm even after the unit has been off. A five-gallon bucket is ideal, but any container that holds at least two quarts will work.
Wear gloves if you have them, because the water may be warm enough to sting. Make sure the area around the valve is clear of clutter so you can see what you're doing and move quickly if needed. If the unit is mounted in a tight space like a closet, open the door fully and position your bucket before you start.
Do not open the valve if anyone is standing directly in front of the unit or if there are electrical outlets or panels within a foot of the valve opening. Water and electricity do not mix.
Open the Valve Slowly to Release Pressure
Locate the lever or button on the valve body. On most Navien models, this is a small red or black lever that you pull outward or upward, or a button you press inward. Some older models use a small flathead screw that you turn counterclockwise. Check your manual if you are unsure which direction to move it.
Open the valve slowly at first—turn the lever or button only a quarter turn, or press the button in just halfway. You will hear a hiss as air and pressure escape. Let it hiss for a few seconds, then open it the rest of the way. This gradual approach prevents a sudden spray and lets you control the flow.
Water should begin flowing into your bucket within a few seconds. The flow may be fast at first, then slow down as the pressure inside the valve drops. Keep the valve open until the water stops flowing completely, which usually takes 30 seconds to two minutes depending on how much pressure was built up.
Close the Valve and Check for Leaks
Once the water stops flowing, close the valve by pushing the lever back to its original position or turning the button back out. Do this firmly but do not force it—the valve should close smoothly with gentle pressure. If it feels stuck or gritty, stop and do not force it; call a technician instead, because the valve seat may be damaged.
Wait 30 seconds, then look at the valve opening. A single drop or two is normal as the valve seat settles, but if water is dripping steadily, the valve did not seal completely. This usually means sediment or mineral buildup is preventing the valve seat from closing fully. Try opening and closing the valve one more time to see if that clears it.
If the drip continues after a second attempt, the valve needs professional service. Do not try to disassemble it yourself—pressure valves are precision parts and opening them can damage the internal seal.
What to Do If the Valve Will Not Open
If the lever does not move or feels stuck, do not force it. Stuck valves usually mean mineral buildup or corrosion inside the valve body, which is common in hard water areas. Forcing it can break the lever or damage the internal mechanism.
Instead, turn off the Navien unit at the power switch and let it cool for 30 minutes. Then try the lever again with steady, gentle pressure. If it still will not budge, spray a small amount of penetrating oil like WD-40 around the lever base, wait 10 minutes, and try again.
If the valve remains stuck after these steps, contact a Navien-certified technician. A stuck pressure valve can indicate a larger problem with the unit's internal pressure regulation, and a professional should inspect it before you use the heater again.
When to Drain the Valve as Part of Regular Maintenance
Drain the pressure release valve once every six months as part of routine maintenance, even if you do not see water dripping. This keeps the valve seat clean and prevents mineral buildup from sealing it shut. If you live in a hard water area, drain it every three months instead.
Also drain the valve before you shut down the unit for an extended period—more than two weeks—such as when closing a seasonal home or preparing for a long vacation. Draining it removes the pressure that can build up while the system sits unused, which reduces the risk of the valve leaking when you turn the unit back on.
If you notice water dripping from the valve between scheduled drains, drain it when ready. A persistent drip means pressure is building up faster than normal, which can indicate a problem with the expansion tank or the unit's internal pressure regulation.
Frequently Asked Questions
Can I drain the pressure valve while the unit is running?
No. Always turn off the Navien unit and wait at least 15 minutes before opening the pressure valve. Opening it while the unit is heating will release hot water and steam, which can cause burns. The unit must be off and cooled so the water inside is safe to handle.
How much water should come out when I drain the valve?
Usually between one and three cups, depending on how long the unit has been sitting and how much pressure built up. If more than a quart flows out, or if the water is very hot, the unit may have a pressure regulation problem and you should have it inspected by a technician.
What if the valve lever breaks off when I try to open it?
Stop when ready and do not try to open the valve further. Turn off the unit and contact a Navien technician. A broken lever means the valve cannot be operated safely and the unit should not be used until the valve is replaced.
Is it normal for a small amount of water to drip after I close the valve?
A drop or two in the first minute is normal as the valve seat settles. Steady dripping after that means the valve did not seal, usually from mineral buildup. Try opening and closing it once more. If it still drips, the valve needs professional service.
Do I need to turn off the water supply before draining the pressure valve?
No. You only need to turn off the power to the Navien unit itself. The water supply can stay on. Draining the pressure valve does not affect the water lines—it only releases pressure from inside the valve body.