Signs Your Drain Is Blocked or Collapsed (and What to Do)
By the Urgent Drainage Solutions teamPublished Updated 6 min read
Slow water, gurgling and bad smells usually mean a blockage. Sinking ground, damp walls and repeat blockages can point to a cracked or collapsed drain.
Most blocked drains announce themselves with slow-draining water, gurgling, bad smells or waste backing up. A damaged or collapsed drain shows the same symptoms, plus warning signs outside the house: blockages that keep coming back, sunken or damp ground, damp patches on walls and rats. If you see those, get the drain checked with a CCTV camera before more damage is done.
This guide lists the signs, explains what usually causes each one and sets out the safe first steps to take.
What are the signs of a blocked drain?
Severn Trent lists the classic symptoms of a blockage:
- a toilet that flushes slowly or fills up before draining;
- sinks, baths and showers that drain slowly;
- bad smells from plugholes, gullies or inspection covers;
- waste water backing up into the property or out of an outside gully.
Checkatrade adds a few more:
- gurgling noises from plugholes or the toilet;
- damp around leaking joints;
- overflowing gullies or standing water outside;
- flies and other insects gathering around outside drains.
A single slow sink usually means a local blockage in that waste pipe, often hair, soap or food. When several fittings are slow at once, or an outside gully overflows while you run water indoors, the blockage is further down the main drain.
What are the signs of a collapsed or damaged drain?
A cracked or collapsed pipe blocks easily, because waste catches on the broken section. It can also leak into the ground. Checkatrade's collapsed drain guide highlights sinking ground, a sewage smell, slow drains, damp and damage to the property. MyJobQuote also points to damp patches or mould on internal walls and sunken or damp ground outside.
Other warning signs drainage engineers look out for:
- Blockages that return soon after clearing. A drain that needs unblocking again and again usually has a defect holding debris.
- An inspection chamber filling with water. If the chamber is full, the pipe downstream of it is blocked or broken.
- A strip of greener grass along the drain run. Some drainage firms point out that a leaking pipe can water the lawn above it.
- Rats. Rentokil links rat activity with persistent blockages and damaged pipes, because rats use cracks to get in and out.
Blocked or damaged: how can I tell?
| What you notice | More likely a blockage | More likely damage |
|---|---|---|
| One slow sink or bath | Yes | Rarely |
| Several fittings slow at once | Yes, in the main drain | Possibly |
| Problem returns within weeks of clearing | Possibly | Yes |
| Sewage smell outside with no obvious overflow | Sometimes | Yes |
| Sunken, soft or damp ground over the drain | No | Yes |
| Damp patches or mould on internal walls near a drain | No | Yes |
| Rats around the house or garden | Sometimes | Yes |
The table is a guide, not a diagnosis. Blockages and damage often go together: a displaced joint catches wipes and fat, and a long-standing blockage can put pressure on weak joints.
What causes drains to block or collapse?
The common causes are well documented:
- Things that shouldn't go down the drain. Severn Trent says pipes are "only designed to carry human waste, wastewater and loo roll". Wet wipes, sanitary items and fats, oils and grease are the usual culprits. See our guide to what not to flush.
- Kitchen and bathroom waste. Checkatrade lists food waste, coffee grounds, hair and soap residue.
- Tree roots, freezing and age. Roots find their way into cracks and joints, and older pipes wear out. Read more in our guide to tree roots in drains.
- Old or disused pipes. Rentokil points to cracked old clay pipes and uncapped disused pipes.
- Displaced joints. Ground movement can push pipe sections out of line, leaving a lip that catches debris. It is one of the standard defects recorded in a camera survey.
Pitch fibre pipes
Many homes built after the Second World War have pitch fibre drains. The Financial Ombudsman Service describes pitch fibre as "wood cellulose impregnated with tar", popular between the 1950s and 1970s, and notes that many insurance policies don't cover it. Industry sources say it tends to deform into an oval shape under load and can blister and delaminate when exposed to hot water or fats. Careless high-pressure jetting can make a weakened pitch fibre pipe worse, so it needs an engineer who recognises it. The usual fix is to re-round the pipe and then reline it.
What should I do first?
Safe first steps while you wait for help:
- Stop running water into the affected drain. Every flush adds to the backlog.
- Check with your neighbours. Severn Trent's rule of thumb is that if neighbours are affected too, the problem is likely to be in the public sewer, which is the water company's responsibility. Our guide to who is responsible for blocked drains explains the split.
- Look, don't dig. Wearing gloves, you can lift a light gully grate to see whether it is full. Don't lift heavy or stuck manhole covers, and keep children and pets away from open chambers.
- Avoid mixing chemicals. Never combine different drain cleaners. They can react dangerously and won't fix a structural fault.
- Treat overflowing water as contaminated. Keep skin contact to a minimum and wash hands thoroughly.
- Tell your insurer early if you suspect damage. The Financial Ombudsman says you should contact your insurer before repairs start, or keep photos, a detailed report and an itemised bill if you can't.
How is a damaged drain confirmed and repaired?
A CCTV drain survey is the only reliable way to see inside the pipe. The camera shows cracks, fractures, displaced joints, roots and deformation, and records exactly where each defect is. That tells you whether the drain simply needs clearing or needs a repair.
Repair options depend on the damage:
- Patch repair for a single crack or open joint.
- Relining, where a resin liner forms a new pipe inside the old one without digging.
- Excavation and replacement where the pipe has collapsed or is badly deformed.
Our guide to drain relining vs excavation compares the options. As a rough market guide, MyJobQuote puts a typical collapsed-drain repair at around £850 and a fully collapsed drain at £1,000 to £3,000, while Checkatrade's collapsed drain guide quotes £295 to £775 per metre. The real cost depends on depth, access and what sits on top of the pipe.
When to call a professional
Call a drainage engineer if a blockage doesn't clear with basic steps, if it keeps coming back, or if you see any of the damage signs above. Urgent Drainage Solutions carries out drain repairs, blocked drain clearance and CCTV surveys across Nottinghamshire, Derbyshire, Leicestershire and Lincolnshire. Unblocking starts from £95 + VAT, CCTV surveys from £120 + VAT, and there is no call-out fee. We agree the price before any work starts, and our repairs (lining, patching and pipe replacement) come with a 12-month guarantee.
We're open 7 days, 6am to 8pm, with emergency call-outs 365 days a year. Book online or call 07300 600 950. If water is coming into your home now, see our emergency drainage page.
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