Airlock in Your Pipes? How to Clear It
A spitting, coughing tap after plumbing work is usually trapped air.
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.
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