Glossary · Plumbing and water
What is an airlock in pipes?
An airlock is a pocket of air trapped in a water pipe that blocks or restricts the normal flow of water. It shows as weak or no flow from a tap, gurgling or banging pipes and, in a heating system, cold spots on radiators. Running the taps often clears it, and bleeding radiators clears one in heating.
Key points
- Signs include a weak or absent flow, gurgling or sputtering, uneven pressure and banging pipes.
- Airlocks typically form at the highest point of a system, so check the highest or most distant tap.
- After a supply interruption, spluttering taps should clear if you run them for a couple of minutes, says Thames Water.
- Yorkshire Water suggests turning the stop tap off and on three or four times with a cold tap running to clear air or sediment.
- If neighbours have water and you do not after an incident, Thames Water says you may have an airlock and offers a technician visit.
What causes an airlock
Water fills a pipe completely and flows as one column. If a pocket of air gets in, it can sit in a bend or high point and block or slow the water. WaterSafe describes an airlock as air trapped in the plumbing system, blocking the normal flow of water.[1]WaterSafe, How do you remove an airlock from water pipes?
WaterSafe lists several ways air gets in. Poor installation, such as incorrect angles or a lack of venting, can let air collect. Leaks, even small ones, can let air in. Sudden pressure changes after maintenance can trap air. Draining and refilling pipes quickly or without proper venting can also cause one.[1]WaterSafe, How do you remove an airlock from water pipes?
You will often meet an airlock after the water has been off. Thames Water says that after an incident the water may splutter out of your taps when it first comes back, and this should clear if you run the taps for a couple of minutes.[2]Thames Water, After an incident happens
Signs, and what you can check yourself
WaterSafe lists these signs.[1]WaterSafe, How do you remove an airlock from water pipes?
| Sign | What you notice |
|---|---|
| Low or no flow | A weak stream, or nothing from the tap |
| Gurgling | Sputtering or gurgling as water forces past the air |
| Uneven pressure | Some outlets weak, others normal |
| Banging | Thumping when air hits parts of the plumbing |
| Cold spots on radiators | In a heating system, hot water not circulating properly |
Work through the simple steps first. Open the affected tap slightly so the water flows and pushes air out. WaterSafe says airlocks typically form at the highest point, so check the most distant or highest tap, and it suggests starting with the lowest tap and working up.[1]WaterSafe, How do you remove an airlock from water pipes? Repeat if it does not clear first time.[1]WaterSafe, How do you remove an airlock from water pipes?
Yorkshire Water gives a stop tap routine. With the main cold kitchen tap on, turn the internal stop tap off and on three or four times, then make sure it is fully open and turn it back slightly to avoid seizing. The water may cough and splutter, but this often brings the water or the pressure back.[3]Yorkshire Water, No water or low water pressure? See stopcock.
For a heating system, WaterSafe says the airlock is cleared by bleeding the radiators.[1]WaterSafe, How do you remove an airlock from water pipes? Vaillant describes gurgling noises as air trapped in the system and says bleeding radiators is the simplest way to deal with them.[4]Vaillant, Why is my boiler making noise? Radiator bleeding is a job a householder can do, but if you are unsure, ask your engineer. Do not open the boiler or touch gas pipework. HSE says anyone employed to work on gas appliances in domestic premises must be a Gas Safe registered engineer.[5]Health and Safety Executive, Domestic gas: frequently asked questions
When to call a plumber
If the taps and stop tap routine do not help, or the airlock keeps coming back, call an approved plumber. A repeat airlock can mean a leak or a pipework fault. If you suspect air getting into a heating system repeatedly, see radiator not heating up and radiator cold at the bottom.
If your neighbours have water and you have none after an incident, Thames Water says you may be experiencing an airlock and will arrange for a technician to attend.[2]Thames Water, After an incident happens For wider low pressure causes, read low water pressure.
Example
After a road works shutdown in Pudsey, Leila turns her taps on and the kitchen tap splutters, then runs weakly. She runs the taps for a couple of minutes, starting at the lowest, and the flow steadies. The bathroom tap upstairs still gurgles, so she runs it for a few minutes more. It clears. Had it not, she would have tried the stop tap routine and then called a plumber.
What people get wrong
Many people assume any weak flow is an airlock and keep running taps for hours. A weak flow can also be caused by works in the area, a frozen pipe or a leak. Check the cause list before assuming air is the problem.
The other mistake is to try fixes that go beyond what a householder should do. WaterSafe describes methods such as connecting hot and cold taps with a hose, and these are best left to an approved plumber.[1]WaterSafe, How do you remove an airlock from water pipes?
The bottom line
An airlock is air trapped in a pipe that blocks the flow of water. It shows as weak flow, gurgling and banging, and cold spots on radiators in a heating system. Run the taps, try the stop tap routine and bleed radiators for a heating airlock. If it keeps returning, call an approved plumber, and leave anything to do with gas to a Gas Safe registered engineer.
Common questions
What are the signs of an airlock?
WaterSafe lists low or no flow, gurgling or sputtering sounds, uneven pressure, banging noises, and in a heating system cold spots on radiators. Several of these also have other causes, so check for leaks and works in your area as well.
How do I clear an airlock?
WaterSafe says to open the affected tap slightly to let water push the air out, starting with the lowest tap and working up. Yorkshire Water suggests cycling the internal stop tap three or four times with a cold tap running. Repeat if needed.
Why did I get an airlock after the water was turned off?
WaterSafe says sudden changes in pressure after maintenance can trap air, and that draining and refilling pipes quickly or without proper venting can cause an airlock. Leaks can also let air in.
When should I call a plumber?
If running the taps and the stop tap routine do not clear it, or the problem keeps coming back. WaterSafe says airlocks can result from poor installation, such as incorrect pipe angles or lack of venting, which needs an approved plumber.
Sources
We cite the original source for every figure: government, regulators, standards bodies and manufacturers' own documents. Each one shows the date we last checked it.
- WaterSafe. How do you remove an airlock from water pipes?. Checked 11 November 2026. ↩
- Thames Water. After an incident happens. Checked 11 November 2026. ↩
- Yorkshire Water. No water or low water pressure?. Checked 11 November 2026. ↩
- Vaillant. Why is my boiler making noise?. Checked 11 November 2026. ↩
- Health and Safety Executive. Domestic gas: frequently asked questions. Checked 11 November 2026. ↩