Toilet Gurgling? What It Means and How to Stop It

A gurgling toilet is a sign that air can't move freely through your drain, so it bubbles through the water in the pan instead. The cause is usually one of two things: a partial blockage somewhere downstream, or a vent problem that stops the drain drawing in air. You can often tell which from when the gurgling happens and what the outside manhole looks like. A gurgle on its own isn't an emergency, but a partial blockage tends to get worse, so it's worth tracking down now rather than when the toilet overflows.

Why a toilet gurgles

Every toilet holds a pool of water in its bend. That water seal stops sewer gases coming into the room. When water runs down a drain, it pushes air ahead of it and pulls air in behind it. A properly working system handles this through the soil stack vent, the pipe that runs up and out through the roof, or through an air admittance valve on houses without an open vent.

If the air can't get in or out that way, it takes the easiest route, which is often through the toilet's water seal. That's the gurgle or bubble you hear, sometimes with the water level in the pan bobbing up and down. If enough water is pulled out of the seal, you may also notice a drain smell. Our guide to a sewage smell in the house covers that side of it.

Blockage or vent? How to tell

The common causes

A partial blockage in the toilet or soil pipe

Wet wipes, sanitary products, cotton buds and too much paper build up in the bend or the first stretch of pipe. Water still gets past, but the pipe runs fuller than it should and traps air. This is the most common cause in a single toilet that has started gurgling. See our guide on how to unblock a toilet.

A partial blockage in the underground drain

Fat, wipes, silt and tree roots narrow the drain between the house and the sewer. The first signs are often gurgling toilets and a slow ground floor shower or sink, before anything overflows. Older London terraces often share a run of drain with neighbours, so a blockage further along can affect several houses. Our article on blocked outside drains explains how to check the manhole and gully.

A blocked soil stack vent

The open top of the soil stack on the roof or high on the back wall can be blocked by leaves, a bird's nest, a wasps' nest or a dislodged cage. With the vent blocked, water running down the stack pulls air through the nearest trap, which is often the toilet. The drains themselves flow normally.

A stuck or failed air admittance valve

Many homes, especially extensions, loft conversions and flats, use an air admittance valve instead of an open vent. It's a one-way valve, usually a grey or white cap on top of the soil pipe in a loft, boxing or cupboard. It lets air in when water flows and seals to keep smells out. If the seal sticks shut through dirt, age or being boxed in without ventilation, the drain can't breathe and toilets and basins gurgle.

The sewer running full

If gurgling happens mostly during or after heavy rain, the public sewer may be surcharging, pushing air back up the drain. That's more common in areas with combined sewers that carry both rainwater and foul waste. If a gully or manhole overflows with sewage, report it to your water company. For smells linked to rain, see sewer smell after rain.

What you can check yourself

1. Watch when it gurgles. Run the bath, then the shower, then the kitchen sink, and note which ones make the toilet gurgle and whether they drain slowly.
2. Lift the outside manhole cover. If the channel at the bottom is flowing and clear, the blockage (if any) is upstream, inside the house. If the chamber is filled with standing water, the blockage is further down, towards the sewer.
3. Plunge the toilet. Use a flanged toilet plunger with enough water in the pan to cover the cup. Firm, steady strokes. If the flush improves and the gurgle stops, you've cleared it.
4. Find the air admittance valve, if you have one. Check it isn't sealed inside airtight boxing. Some can be unscrewed and the seal cleaned, but many are simply replaced.
5. Look at the top of the stack from the garden or a window. Don't go on the roof. If you can see debris or a nest, that's a job for someone with the right access equipment.

When to stop using the drains

Stop running water and flushing if:

• the toilet pan fills to the rim or water rises in it when another fixture drains;
• dirty water backs up into a shower tray, bath or ground floor sink;
• an outside gully or manhole is overflowing.

Each of these means the drain is blocked below that point, and more water will only come out at the lowest opening, usually the ground floor toilet or shower.

When to call a plumber

Call a plumber if plunging doesn't stop the gurgle, the manhole is full of standing water, more than one drain is slow, or you suspect the vent or air admittance valve. We clear blocked toilets and blocked drains across London with rods and drain jetting, replace failed air admittance valves and repair soil pipes. If a drain keeps blocking or gurgling, a CCTV drain survey shows whether roots, a collapse or a dip in the pipe is the underlying cause.

When you call, tell us when the gurgling happens, which drains are slow and what you saw in the manhole. Our labour is £95 an hour, the £60 call-out is waived when the job runs over 2 hours, and we confirm the price before any work starts. If the blockage turns out to be in a shared or public sewer, we'll tell you so you can report it to the water company.

Frequently Asked Questions