Signs of a collapsed drain (and what to do next)

A collapsed drain is a pipe that has lost its structural shape — cracked, fractured, deformed, or broken open so that the bore is partly or completely obstructed and soil is getting in. It is not the same thing as a blockage, even though the day-to-day symptoms look almost identical. A blockage is something stuck inside a sound pipe and clearing it fixes the problem. A collapse is the pipe itself failing, and no amount of rodding or jetting will do anything except buy a few weeks.

Collapses happen for predictable reasons: age in Victorian clay runs, ground movement in shrink-swell clay soils, tree root pressure forcing joints apart, heavy vehicle loading over a shallow pipe, poor bedding when the run was originally laid, and corrosion or deformation in early concrete and plastic pipework from the post-war building boom.

The clearest indicator is repeat blockages in the same place. A drain that blocks once is bad luck; a drain that blocks three times in a year has something wrong with it. Debris catches on a displaced joint or a fractured section, builds up, blocks, gets cleared, and starts the same cycle again. Slow drainage that never quite goes away between clearances points the same way.

Then there are the signs that soil is entering the pipe. A dip, soft patch or sinkhole in a lawn, path or driveway along the drain line means material is being washed away underground. Cracks appearing in a wall or a path following the run, or a section of ground that stays damp when everything around it has dried, suggest the same. Persistent damp or a sewage smell at low level inside a property, and rats appearing where they never used to, are both strong indicators of a broken pipe — rodents get in through a fractured drain more often than any other route.

Finally, unusually lush grass in a strip across an otherwise even lawn is a genuine giveaway. Waste water leaking from a broken run fertilises the ground above it.

You can't reliably tell from the surface, and this is exactly where money gets wasted. The distinguishing test is what happens after a proper clearance. If the drain runs freely and stays clear for months, it was a blockage. If it starts slowing again within days or weeks, something structural is catching material and you need to see inside the pipe.

The only way to confirm a collapse is a CCTV drain survey. A camera run through the pipe shows the defect, its type, its depth and its distance from the access chamber, and a sonde locates it precisely from the surface. That location detail is what determines whether a repair can be done from inside the pipe or whether the ground has to come up — and it's what stops anyone excavating in the wrong place.

The good news is that a collapse rarely means digging up a garden any more. Where the pipe still holds its shape well enough to take a liner, a localised patch repair over a cracked joint or a fractured section is typically a few hundred pounds and takes a few hours, with no excavation at all. Where the damage runs along a length, a cured-in-place liner can reline the whole run from an existing chamber — more expensive, but still no-dig.

Full excavation and replacement is reserved for pipes that have genuinely lost their shape: sections that have caved in, been crushed, or dropped out of alignment so far that a liner can't be pulled through. That's the costly option, and it's the reason a survey should always come before a quote to dig. If a contractor recommends excavation without having put a camera down the pipe first, get a second opinion.

If the collapsed section lies within your property boundary and serves only your property, it's yours to repair. If it lies beyond the boundary, or it's a shared run serving several properties, it most likely transferred to the regional sewerage undertaker in 2011 and repairing it is their job.

Buildings insurance is worth checking too. Many policies include accidental damage or a specific underground services section that covers drain collapse, and most insurers will want CCTV evidence, a location reference and a written report before they'll consider a claim. Getting the survey done properly at the start means you have the documentation for whichever route ends up paying.

Stop paying for repeat clearances. Get a CCTV survey with a written report and footage, establish where the defect is and which side of the boundary it sits on, and then make the repair decision from evidence rather than guesswork. If soil is visibly moving — a sinkhole, a dropping path, a widening crack — treat it as urgent, because the void underground grows quietly and the surface gives way suddenly.

In the meantime, ease the load on the run: keep fats and wipes out of it, and avoid parking heavy vehicles over the pipe line if you know roughly where it runs.