An airlock in pipes shows up as spluttering, gurgling, or a tap that stops flowing, usually at one outlet rather than the whole house. Clear it by running a hose between the affected tap and a mains-fed tap to push water (and air) through, or by opening and closing the tap repeatedly. If it keeps coming back with no obvious cause, that pattern can point to air being drawn in through a leak, not a one-off fault.
An airlock is a pocket of trapped air sitting inside a water pipe, blocking or disrupting the flow. It is usually harmless and easy to clear once you know the trick, but a recurring airlock is worth paying attention to, because it isn't always "just air". This guide covers how to recognise one, how to clear it safely, and when repeated airlocks are actually a symptom of something else in the system.
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Symptoms: is it really an airlock?
An airlock has a fairly distinctive signature, which helps separate it from other plumbing problems before you start pulling out hoses and wrenches.
- A tap splutters, coughs or spits air before water comes through.
- Flow surges between strong and weak, or stops and starts, at a single tap or shower.
- One outlet stops working altogether while others in the house are fine.
- It often follows work on the plumbing: a new appliance fitted, a tank drained, a repair completed, or the water having been off for a period.
- A gurgling noise sometimes comes from the pipework itself as the pocket of air shifts.
The key pattern is that it's usually localised to one outlet or one part of the system, and it tends to start suddenly after something disturbed the pipework, rather than gradually worsening over weeks.
What causes an airlock
Air gets into a water system in a handful of predictable ways:
Common causes
- Draining and refilling the system, whether for a repair, a burst pipe, or seasonal drain-down on a second home, lets air into pipework that then has to work its way back out.
- Work on the plumbing, such as fitting a new tap, cylinder or appliance, often introduces a pocket of air near the new connection.
- A drop in the header tank on older gravity-fed systems, if the tank has run low, can pull air into the feed.
- Uneven pipe runs with high points create a natural spot for air to collect, since air rises and gets trapped at the top of a loop.
Most of these are one-off events. Once the air has worked through and out of a tap, it typically doesn't return unless the system is disturbed again.
How to clear an airlock safely
There are two widely used methods, and both work by using mains pressure to push the air out ahead of the water.
Method 1: the hose method
- Get a length of hose (a washing machine or garden hose works) with connections that fit both taps.
- Connect one end to the tap that has the airlock, and the other end to a nearby tap that you know is mains-fed and working properly, usually the kitchen cold tap.
- Open the mains-fed tap first, then slowly open the affected tap. Mains pressure pushes water backward through the affected pipe, forcing the trapped air out.
- Let it run for a minute or two once water flows steadily, then close both taps and disconnect the hose.
Method 2: the on-off method
For a smaller airlock, sometimes turning the affected tap fully on, then off, then on again several times in quick succession is enough to dislodge the pocket of air and let it clear on its own.
When it isn't an airlock at all
A few other problems get mistaken for airlocks because they share some of the same symptoms. Weak flow at every tap in the house, rather than one outlet, points to low water pressure rather than trapped air. A part-closed stopcock, a restriction in the supply pipe, or a leak reducing pressure elsewhere in the system can all produce a steady weakness that looks similar at first but behaves differently: it's constant rather than a sudden splutter that clears once air escapes.
When a recurring airlock means a leak
A single airlock after draining a system or fitting a new appliance is normal and expected. What's worth taking seriously is an airlock that comes back repeatedly, at the same tap, with no obvious trigger each time. Air doesn't usually re-enter a sealed, full system on its own. If it keeps happening, something is letting air in continuously, and one possibility is a small leak or loose joint on the pipe run that lets air in as pressure drops, even while occasionally letting water out too.
Other signs worth combining with a recurring airlock: an unexplained rise in your water bill, the sound of water running when every tap is off, or a damp patch that doesn't tie to an obvious cause. On their own, none of these confirm a leak, but together with repeated airlocks they're a reasonable basis to get plumbing leak detection done, using non-invasive methods like acoustic sensors and tracer gas to check the run rather than guessing and re-bleeding the same tap every few weeks.
Airlocks in Cornwall and Devon properties
Older cob cottages and granite-built homes across Cornwall and Devon often have plumbing that has been extended and altered over decades, with pipe runs that rise, fall and double back in ways a modern install never would. That geometry makes airlocks genuinely more common here than in a newer estate house with straight, well-planned pipework. Second homes and holiday lets that get drained down over winter are another frequent source, since refilling the system after months empty almost always introduces some air. We see this most weeks in spring, when seasonal properties come back into use and taps splutter for the first time in months.
Frequently asked questions
What are the signs of an airlock in a water pipe?
Spluttering or gurgling from a tap, a burst of air followed by water, a shower that surges between strong and weak, or a tap that stops flowing altogether are typical signs. It usually affects one outlet rather than the whole house, and often follows work on the plumbing, a drained system, or a period the water was off.
How do you clear an airlock in a water pipe yourself?
A common method is connecting a hose between the affected tap and a mains-fed tap (such as the kitchen cold tap), then opening both so mains pressure pushes water through and forces the air out. Alternatively, opening the affected tap fully for a minute, then turning it off and on repeatedly, can dislodge a smaller airlock.
Can an airlock damage my pipes?
An airlock itself doesn't damage pipework. The risk is what you do to try to clear it: over-tightening fittings, forcing a hose connection, or repeatedly hammering a tap can create new problems. If a careful attempt doesn't clear it, it's better to get a plumber to look rather than keep forcing it.
Why does my airlock keep coming back?
A one-off airlock after work on the system is normal. One that returns every few days or weeks, with no obvious cause, suggests air is being drawn in continuously, which can happen if a pipe has a small leak on the suction side of a pump or a loose joint that lets air in as well as letting water out.
Is an airlock the same as low water pressure?
No. An airlock causes spluttering, surging or a total stop at one outlet, often suddenly. Low water pressure is a steady, ongoing weakness across some or all taps. If you have a general weak flow rather than air and spluttering, that points to a pressure problem rather than trapped air.
Should I call a plumber or a leak detection specialist for an airlock?
A straightforward airlock after works or a drained system is a plumbing job. If the airlock keeps recurring with no clear cause, or comes with a rising water bill, damp patches, or the sound of running water when nothing is on, that's worth investigating as a possible leak rather than repeatedly bleeding the same tap.
Airlock keeps coming back? Let's rule out a leak
If clearing the same airlock has become a regular chore, we'll check whether air is entering through a hidden leak, using non-invasive methods across Cornwall and Devon.
Call Dickie on 07822 025 911 No Find, No Fee on residential leak detection (subject to terms)