Bleed Water Lines After a Shutoff: Turn Water Back On Safely

After you turn off and then reopen the main water valve—for a repair, a temporary shutoff, or because a leak detector’s valve has closed itself—there is usually air in the pipe between the main valve and the taps in your home. You bleed the water line by opening the taps one at a time, starting at the lowest point in the house, and letting each tap run until the water flows steadily instead of sputtering. This is usually done within a few minutes, and a sputtering start or a single bang when you turn the water back on is not a problem in itself.

• Start at the lowest tap in the house and work your way up, one tap at a time.
• Let each tap run until the flow is steady before moving on to the next one.
• A bang that keeps coming back after bleeding the line is more often a sign of a tap that no longer closes properly than of air in the line.
• With the Hydrion leak detector, you turn the water back on through the Smart Life app, not with a button on the device.

What happens when you turn the water back on

Whenever a pipe is completely shut off and then reopened, the section between the main valve and the tap can contain air. It makes no difference whether you turned off the main valve yourself for a job, or whether the leak detector’s motorized valve closed automatically after detecting an unusual flow. As soon as you open the tap again, the water pushes the air ahead of it, causing the sputtering or spitting at the start, or sometimes a single bang, that you hear at the first tap (source: Huiskeur). That is what happens when the pipe has been empty for a while, and is a normal occurrence in itself. The aim of the routine below is simple: get a steady flow from every tap again, while the banging dies away and the pipes stay dry where they should.

If the main valve itself isn’t cooperating—for example, because it is stuck or you can’t find it right away—that is a different situation from the one described above. You can read where the main valve is usually located and what to do if it is stuck in separate articles, because the rest of this routine is pointless without a working main valve.

The order in which to open the taps

First, open the tap closest to the lowest point in the house about halfway, and let it run until the water flows in a steady stream instead of coughing or spitting (source: Toppex). Then go through the other taps one by one instead of opening them all at once, so the remaining air always has one clear way out rather than being pushed back and forth through the system (source: Loodgieters Kwartier). At the end, flush the toilet once or twice as well, to bleed its supply line too.

Why you start at the lowest point

Air naturally rises to the top of a filled pipe, so a tap on the ground floor or in the basement gives it the shortest and most predictable way out. If you start upstairs instead, air that was already on its way out can be pushed back into the pipe when you open another tap, making the process take longer than necessary.

What to do if a tap keeps sputtering

If a tap is still flowing unevenly after a minute or two, simply let it run a little longer instead of turning it off and starting again later: stopping gives the air a chance to move around again. If the same tap is still doing this after a few minutes while the others have been flowing steadily for some time, move on to the next tap and come back to this one once more at the end.

Why the pipe bangs or knocks while you bleed it

The bang you hear while bleeding the line happens when an air bubble moves through the pipe and collapses against a tap that is closing or a sudden stop in the flow. This effect lessens as there is less air in the pipe, so it should gradually disappear during the routine rather than get worse.

If the banging comes back after the pipes have been flowing clearly for some time, the usual explanation is generally not that there is air in the line again, but that a tap somewhere in the house is no longer closing completely (source: Loodgieter.nl)—that is the time to check it before repeating the entire bleeding routine.

If the banging keeps coming back after bleeding the line

If the sputtering or banging doesn’t go away after you have gone through the routine once or twice, plumbing references generally recommend having a plumber inspect the specific tap or connection rather than repeating the bleeding process over and over (see also Huiskeur). Whether a water hammer arrestor or replacing a tap is the right solution depends on what the plumber finds on site; it is not a decision you can make in advance from a distance.

It is also a good idea to visually check the joints and the areas under appliances for a slow drip after every shutoff and reopening, because the vibration from bleeding the line can sometimes loosen an older connection a little.

Turning the water back on after a leak detector shutoff

With the Hydrion leak detector, the shutoff happens a little differently than with a manual main valve: the motorized valve closes the main line itself within seconds as soon as the device detects an unusual flow, rather than just sending an alert. You don’t turn the water back on with a button on the device itself, but with a tap in the Smart Life app. It is worth checking the flow and usage history in the app first, so you have an idea whether the trigger was caused by a real event—a tap left running or a burst pipe—before you reopen the valve. Once the valve is open again, the same bleeding routine described above applies, because the pipe has been completely idle in the meantime.

The device’s sensitivity in detecting small drips—down to about 0.01 GPM, roughly one drop per minute, within a measurement range of 0.001 to 18.00 GPM—is also precisely why it sometimes shuts off during an unusually high but legitimate flow, for example when filling a large bathtub. This is a deliberate design trade-off, not a defect, and it is useful to know before wondering why the valve closed.

If the valve still shows as offline in the app rather than simply having closed, that is a different problem from the one described above; what to do if the device stays offline applies to that situation. More about how this type of valve works and why it monitors the entire main line instead of a single appliance can be found in the guide to smart leak detectors with automatic shut-off valves.

In practice, bleeding a water line after a shutoff takes just a few minutes: start low, work through the taps one at a time, and let each run until the flow is steady. If the banging keeps coming back afterward, it is more often a tap than air, and calling a plumber is the logical next step. The fact that a device monitors the entire main line and steps in itself when it detects an unusual flow is exactly what caused this situation in the first place—and why it helps to know how to get things flowing smoothly again afterward.