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Why is my drain blocked? The 7 most common causes

Nine times out of ten, a blocked drain comes down to one of seven things. Here is how to spot which one you are dealing with — and what actually fixes it.

Why is my drain blocked? The 7 most common causes

A slow-draining sink, a gurgling toilet or a bad smell drifting up from an outside gully — a blocked drain almost always announces itself before it becomes an emergency. The good news is that most blockages come down to a short list of usual suspects, and once you know what is causing yours, the fix is usually straightforward.

We clear blocked drains across Teesside and the wider North East every single day, and the same causes come up again and again. Here are the seven most common, how to tell them apart, and what it takes to put each one right.

Key takeaways
  • Most blockages are caused by fat, wet wipes, hair, roots, pipe damage or silt — in that rough order
  • A blockage that keeps coming back in the same place usually means roots or a damaged pipe, not a one-off clog
  • Grease and wet-wipe blockages almost always need jetting or rods, not just a plunger
  • If it turns out to be a shared sewer, the water company should fix it — not you

1. Fat, oil and grease (the number one culprit)

Pour a pan of warm cooking fat down the sink and it looks harmless. But as it travels along the pipe it cools, hardens and sticks to the walls — and every bit of grease after it adds another layer. Over months this builds into a solid, waxy blockage that water simply cannot get past. In commercial kitchens the same thing forms a “fatberg” in no time at all.

The fix: hot water and washing-up liquid can shift a very early build-up, but a set-in grease blockage needs high-pressure water jetting to cut it off the pipe walls completely. Rodding alone tends to punch a hole through it that blocks again within weeks.

2. Wet wipes, sanitary items and “flushable” products

“Flushable” wipes are the biggest myth in drainage. Unlike toilet paper, they do not break down — they snag on any small imperfection in the pipe, catch everything that comes after them, and quickly form a dense plug. Sanitary products, cotton buds and kitchen roll do exactly the same.

The fix: a plunger sometimes shifts a very recent blockage, but a wipe blockage in the main run usually needs professional rods or jetting. The only real prevention is the old rule — only ever flush the three Ps: pee, paper and poo.

3. Hair and soap scum

In showers, baths and bathroom basins, hair binds together with soap and shampoo residue into a surprisingly tough clog. It is the most common cause of a slow-draining bathroom, and it builds up gradually so you barely notice until the water is standing around your ankles.

The fix: clearing the trap and using a drain snake handles most bathroom blockages. Fitting a cheap hair-catcher over the plughole prevents almost all of them coming back.

4. Tree and shrub roots

Roots are drawn to the water and nutrients inside drains. They find their way in through the tiniest crack or loose joint, then grow into a dense, hair-like mass that traps debris and eventually cracks the pipe open. If your blockages keep coming back in the same spot — especially in an older property with mature trees or hedges nearby — roots are a prime suspect.

The fix: root ingress needs specialist root-cutting equipment, and afterwards a CCTV survey to see how much damage has been done. Where a pipe is cracked, no-dig relining can seal it without digging up the garden.

5. A collapsed or damaged pipe

Older clay and pitch-fibre pipes crack, sag and eventually collapse with age and ground movement. When that happens, waste catches on the broken section and blocks repeatedly no matter how many times it is cleared. Recurring blockages that no amount of rodding fixes are the classic warning sign.

The fix: there is no plunger for this one — the pipe itself has to be repaired. A CCTV drain survey pinpoints exactly where and how bad the damage is, and the repair is then either no-dig relining or a targeted excavation of just the failed section.

6. Silt, scale and general build-up

Outside drains and gullies slowly fill with silt, grit, leaves and mineral scale washed in over the years. It rarely causes a sudden blockage, but it narrows the pipe until heavy rain overwhelms it and water backs up over the gully.

The fix: a periodic high-pressure jet-clean flushes silt and scale out completely and gets the pipe back to full bore. For businesses and rental properties, scheduling this once or twice a year is far cheaper than an emergency call-out.

7. Not your drain at all — the shared sewer

Sometimes the blockage is not on your property. If more than one property is affected, or the problem is in a shared sewer or the public lateral, it is the water company’s responsibility to fix — not yours, and not at your cost. Plenty of people pay for work that Northumbrian Water should be doing for free.

The fix: this is where honest advice saves you money. If we come out and find the fault sits with the water company, we will tell you straight away and point you in the right direction — we would rather give you the truth for free than charge you for a job that is not yours to pay for.

Need a hand from a local drainage team?

NE Drain Services covers Teesside and the wider North East — fast, fully insured, fixed prices agreed before we start.

FAQs

Related questions

How do I know if my blocked drain is serious?
As a rule of thumb: a single slow sink is usually minor and DIY-friendly, but standing water outside, more than one blocked fixture at once, bad smells or gurgling from the toilet point to a main-drain blockage that needs professional clearing. If it keeps coming back after clearing, get a CCTV survey — that pattern usually means roots or a damaged pipe.
Can I unblock a drain myself?
Often, yes — a plunger, a drain snake or clearing the trap will handle many sink and bathroom blockages. Avoid harsh chemical drain cleaners, which can damage older pipes and rarely shift a serious blockage. If the blockage is outside, in the main run, or keeps returning, it is worth calling us rather than fighting it.
How much does it cost to unblock a drain?
Most standard drain unblocks with NE Drain Services cost between £100 and £200, always agreed as a fixed price before we start. There is no call-out charge, and if the fault turns out to be the water company’s responsibility we will tell you for free.
How quickly can you come out in the North East?
For emergencies we aim to be with you the same day, often within the hour from our Hartlepool base. Just call us 24/7 on 01429 802500.
More advice

Not sure which one you’re dealing with?

Tell us what your drain is doing and we’ll tell you the likely cause and a fixed price — honestly, even if the answer is that it’s the water company’s job.

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