Toilet gurgling or bubbling: what it means

Why a toilet gurgles

The water that sits in the bottom of the pan is a seal. It stops drain air and smells coming into the room. When water runs through the drain, it moves air along with it. In a healthy system, air is let in or out through the vent at the top of the soil stack, or through an air admittance valve, and the water in the pan stays still.

If the drain is partly blocked, the water backs up behind the blockage and squeezes the air in the pipe. The easiest way out for that air is up through the toilet, so you hear bubbling and see the water in the pan rise or rock. If the vent is blocked or the valve has stuck shut, the opposite happens: draining water pulls air in through the toilet trap, you hear a glug, and the water level in the pan drops.

What the timing tells you

Before calling anyone, notice when it happens. The pattern points to the cause far better than the sound itself.

Partial blockage: the most common cause

Wet wipes, even the ones sold as flushable, are the usual culprit in London drains. They do not break down, they catch on joints and rough patches, and they build into a plug with fat and hair. Before a drain blocks completely, it often gurgles for days or weeks.

Check whether other fixtures are draining more slowly than usual. A bath or shower that takes longer to empty, a sink that holds water for a moment before going, or a toilet flush that swirls high before disappearing all point to a narrowing somewhere downstream. If the sinks and bath make the noise as well, our guide to gurgling sinks and baths explains what that pattern tells a plumber.

If you can do so safely, lift the cover of the nearest inspection chamber outside. If there is standing water in it, the blockage is further down. If it is clear but the toilet still gurgles, the problem is between the house and that chamber. Do not use chemical drain cleaners in the toilet: they will not shift wipes, and they make the water hazardous for whoever clears the drain.

Venting problems

Every drain needs air. Houses usually have an open soil vent pipe that runs up the outside wall or through the roof, or an air admittance valve, a small plastic cap on top of the soil pipe inside the house, often in the loft, a boxed-in section or behind the toilet.

An air admittance valve opens to let air in when water drains and closes to keep smells out. When it sticks shut, the toilet trap is pulled instead, and you hear it gurgle and see the water drop. When it sticks open, you notice a drain smell near the valve. Can a faulty air admittance valve cause drain smells? Our guide explains how they fail and how they are replaced.

An open vent at roof level can be blocked by a bird's nest, leaves or a cage that has come loose. Do not climb onto the roof or up a ladder to check it. A plumber can test the stack from below and, if the vent needs clearing, use proper access.

If the water in the toilet pan keeps dropping and you notice a sewer smell in the bathroom, keep the door closed, open a window and pour a jug of water into the pan to restore the seal until the cause is found.

Flats and shared stacks

In a block of flats, toilets and baths on several floors usually drain into one shared soil stack. If your toilet gurgles when someone above or next door uses their bathroom, the stack itself may be partly blocked or not properly vented. Clearing your own toilet will not fix it.

Tell your landlord or managing agent, and note which flats seem to be affected and when. Our guide to drain smells across several flats explains how a shared-stack survey is arranged. Blockages low in a shared stack are the ones that end with a ground floor toilet overflowing, so do not leave it.

What you can safely try

Do not rod the drain from the toilet, do not remove or cap an air admittance valve and do not climb up to the vent. If the toilet starts to fill and not drain, turn to our guide for a toilet overflowing.

• Flush once and watch: if the level rises high and drains slowly, plunge the toilet gently with a flanged toilet plunger.
• Run the bath or shower for a minute and see whether the toilet reacts. That tells the plumber which branch is involved.
• Check the outside chamber for standing water, if the cover lifts easily.
• Stop flushing wipes, cotton buds and sanitary products straight away.
• Keep a note of when it happens and what else was draining at the time.

What an engineer will check

An engineer will first run water through each fixture to reproduce the gurgle and see which pipes are involved. They will lift the inspection chambers to find where the water is backing up, then clear the blockage with drain rods or water jetting. If the drain is clear but the gurgling carries on, they will test the air admittance valve and the vent, and check that newer bathrooms or extensions were connected with enough ventilation.

If the drains keep narrowing, a camera survey will show whether there is a dropped joint, a root, a collapse or a build-up of scale that needs a repair rather than another clearance. Our page on why drains keep blocking covers what those surveys usually find.

Book a drain check before it blocks

Loyal Plumbers covers London and everywhere inside the M25, 24 hours a day, with 10 vans on the road. We clear blocked drains and toilets, replace air admittance valves and carry out CCTV drain surveys when a problem keeps coming back. Call 020 4652 8585 and tell us when the toilet gurgles and what else was draining at the time.

Our call-out charge is £60, and the engineer explains what they have found and what the work involves before starting. You can read more on our toilet unblocking page and our CCTV drain survey page.