Airlock in Your Pipes? How to Clear It

Connect the airlocked hot tap to a working cold tap with a short hose, secure both ends, then turn the cold on for 20-30 seconds. Mains pressure pushes the trapped air back through the system. Turn the hot off first, then the cold, or you will siphon dirty water back into the main.

Published 13 July 2026 · Written by the Emergency Plumb engineers

How to tell it is an airlock

One tap spits, coughs and dies while the others run fine, usually just after work on the system or a drained tank refilling. If every hot tap is dead the problem is upstream at the boiler or cylinder, not air.

The hose trick

Connect a short hose between the mains cold tap and the affected hot tap, open both for thirty seconds, and mains pressure pushes the air plug back up the pipe. Two or three rounds usually clears it.

If it keeps coming back

Recurring airlocks mean pipework laid without proper falls, or a tank fill problem letting air draw in. That needs a survey rather than a weekly hose ritual, and it is a small job to put right.

Why airlocks form where they do

Air enters when the system is drained and refilled, when a tank runs low, or when work is done on the pipework. It then collects at the high point of a run, and because gravity-fed hot water has little pressure behind it, that pocket is enough to stop the flow entirely. Mains-pressure systems clear themselves; gravity systems do not.

The hose method, step by step

Connect a hose from the mains cold tap to the affected hot tap and secure both ends. Open the hot tap, then the cold, and let mains pressure push back through the hot run for around thirty seconds. Close the cold first, then the hot. Mains-to-hot connections must be temporary and removed afterwards, leaving one in place is a Water Regulations breach.

When it is not an airlock

If every hot outlet is dead rather than one, the problem is upstream, an empty cold tank, a failed float valve, or a blockage at the tank outlet. If it returns within days, air is being drawn in continuously, which usually means the cold tank is running low or the vent pipe is discharging back into it. Both need looking at rather than repeatedly bleeding.

Common questions

Airlock in Your Pipes? How to Clear It, your questions

How do I know it is an airlock and not something else?

An airlock spits and splutters, gives inconsistent flow, and usually affects one tap - typically a hot tap on a gravity-fed system. If every outlet is weak, it is more likely low pressure or a partly closed valve than air.

Why do airlocks happen in the first place?

Air gets in whenever the system is drained and refilled - after a repair, a new radiator, or a period with the water off. Gravity-fed systems fed from a loft tank are far more prone to it than mains-pressure systems, because there is less pressure to push air along.

Can an airlock clear on its own?

Sometimes, with repeated use, but it can also migrate and lodge somewhere worse. If a tap has been spluttering for more than a few days it is worth clearing properly rather than waiting.

What if the hose method does not work?

Persistent airlocks usually mean a pipe run with a high point that traps air, or an undersized feed. That needs the pipework looking at rather than another attempt with a hose - repeated forcing can loosen old joints.