Gurgling noise from drains and plughole

Gurgling from a plughole when water drains indicates a partial blockage or ventilation problem in the drainage system. Air is being drawn through the trap water seal, which causes the gurgling sound.

Check the drain for partial blockage — pour boiling water down the drain followed by drain cleaner. A partial blockage causes slow drainage and allows air to bypass the water seal.

If the gurgling only happens when another fixture drains (e.g. the bath gurgles when the toilet is flushed), the soil stack vent may be blocked. The stack vent is the vertical pipe that terminates above the roofline — check for bird nests or debris blocking the open end.

Air admittance valves (AAVs) are used on UK drainage systems instead of an open vent in some locations. If the AAV has failed (they can seize shut), it can cause gurgling and even allow sewer gas into the property. AAVs cost £5–£20 and are simple to replace.

If clearing the partial blockage and checking the vent does not resolve persistent gurgling, a drainage CCTV survey will identify any root intrusion or collapsed pipe sections.