Why is my drain blocked? Causes, what to try first, and when to stop

The short answer

Fat, wipes, hair and waste cause most blocked drains. Roots and broken pipes cause the rest. Try a plunger first, then warm water and washing-up liquid. Stop if more than one fixture has trouble, because the fault is then further along. Stop too if water backs up outside.

What the symptoms tell you

Not every slow drain is the same fault, so the signs give you a clue before you try anything.

• Gurgling. Air is trapped by something that restricts the flow.
• One slow sink or bath. The blockage is probably close to that fixture.
• Several fixtures backing up. The blockage is further along the shared pipe.
• An overflowing gully outside. The blockage lies in the underground run.

The further away the fault, the less a plunger will do. A drain rod or a camera may suit better, since they reach further.

What really blocks drains

Water companies see the same causes again and again. While each firm has its own page, Thames Water’s Bin it page names wipes and fats, oils and grease. It says only pee, poo and toilet paper belong in the toilet. It adds that even flushable wipes cause blockages.

Fat is a common problem in kitchens. Let cooking fat cool and set, then put it in the bin. The same source says hot water and washing-up liquid do not stop fat building up, since it sets again further down.

What to try first

For one slow fixture with no other signs, work through these steps in order, because each is gentler than the next.

1. Plunger. Cover the overflow, add enough water to seal the cup, and pump firmly.
2. Warm water and washing-up liquid. Pour it in slowly to loosen grease.
3. Drain auger. A hand-turned auger can hook out hair or a clump of waste.
4. Stop. If none of these works, do not escalate the tools.

Use hot tap water rather than boiling water, because boiling water can harm some fittings.

What not to do

Strong chemical drain cleaners are sold as a quick fix. They rarely clear a real blockage, yet they can harm old pipes and fittings. They are also hazardous if the drain does not clear. Read the label, wear gloves and keep children away. If you are unsure, skip them and call a plumber.

Never push rods or tools into a drain you cannot see. You may push the blockage further, or you may damage a joint.

When to stop and get help

Some signs mean the fault is beyond a plunger.

• More than one fixture is affected.
• An outside gully or manhole is overflowing.
• The same spot blocks again and again.
• Your only toilet is out of use, or waste is backing up.

A repeat blockage often has a cause in the pipe, such as roots. A CCTV drain survey shows the cause. Our guide to what a CCTV drain survey shows explains the report. Meanwhile, the cost guide sets out typical prices.

If sewage is backing up into the house, treat it as urgent, because it is a health risk. Our emergency plumber service takes requests through the form at any hour.

Whose drain is it?

If only your home has trouble, the fault is probably yours. If neighbours have the same problem, it may be a shared drain or public sewer. Read who is responsible for a blocked drain to see the boundary rules. Then see how to report a blocked drain or sewer for the next step.

Blocked gullies and yard drains are a separate case. Our guide to a blocked drain outside the house covers them. Drain faults vary between towns, while blocked drains across the Nene Valley compares four.

Related problems

A toilet that will not flush may not be a drain fault at all. If you have a pump unit, read Saniflo not working. A new bathroom is a good time to check the pipes. The bathroom fitting cost guide explains why. Buyers can see inside the pipes with a pre-purchase CCTV survey.

A bath that runs cold is a different problem from one that drains slowly. If the water drains but is not hot, see no hot water: what to check.

Frequently asked questions

Why does my drain keep blocking?

A repeat blockage in the same place usually has a cause beyond waste, such as roots or a low spot. A camera survey can confirm which, since it shows the pipe.

Can I use drain cleaner on an outside drain?

We advise care, because strong cleaners can harm old pipes. Outside gullies may lead to shared drains. Ask a plumber first.

Is a gurgling drain serious?

It is a warning, because something is restricting the flow. Check for other signs and act early.

Still blocked?

Use the online form and describe the symptoms. Name the fixtures with trouble. Mark it urgent if sewage is backing up. Our blocked drains service covers clearing. You can also browse all our services and the areas we cover. Add your town and a short description, because that helps an engineer get back to you.

In Northampton, see blocked drain help in Northampton. Around Raunds, see plumbers in Raunds. Near Irthlingborough, see plumbers in Irthlingborough. In Rushden, see blocked drains in Rushden and plumbers in Rushden. Each page explains local coverage, while the form works for every town.