Downpipe blockages

How do you clear a blocked downpipe?

Water backing up a downpipe means something is stuck in the bore. Here are the steps that are safe from the ground, and where the ladder work begins.

The short answer

Clear a blocked downpipe from the bottom up: take off the shoe or lift the gully grid, push a flexible rod or a hose up the bore, and flush it until the water runs freely. If the plug sits at the top, in the outlet or a bend, it needs reaching from a tower or ladder. A pipe that is split, or has come away from its brackets, needs replacing rather than clearing.

5 min read · Part of Gutters, soffits & fascias

A hipped red-tile roof on a white-rendered bungalow — A downpipe running down a brick wall to a gully

How to tell where the blockage sits

Run a hose into the gutter above the outlet, or wait for the next shower, and watch the pipe. The symptom points to the place.

Water pours over the gutter's front edge beside the outlet: the plug is at the top, in the outlet or the first bend.
Water sprays from a joint part-way down the pipe: the plug is just below that joint.
Water backs up from the foot and wets the wall: the shoe, the gully grid or the drain beyond is silted.
The pipe stays dry and the gutter empties well: the trouble lies elsewhere on the roofline.

A dark, damp stripe on the brickwork behind a pipe can mean a split in its back, hidden from the garden. That is a different repair from a blockage, so study the wall as well as the pipe, and take a photo of it for the survey. Where the stripe starts only below a joint, the joint is the likelier fault, and where it runs the full height of the pipe, look for a split. A shoe that has dropped away from the gully, or a gully grid packed with silt, also lets water splash back onto the wall.

Clearing it from the ground

Start at the foot, where you can stand on firm ground. Lift out the gully grid and remove leaves, grit and silt from the trap. Pull off the shoe, the angled piece that turns the pipe into the gully, and look up the bore with a torch.

Set a bucket under the opening and wear gloves; the sludge is wet and gritty.
Feed a flexible drain rod, or a length of hose, up the pipe until it meets resistance.
Work the rod gently to break the plug up, letting the debris fall into the bucket.
Flush from the top with a hose held at the outlet, and watch the foot for a steady flow.
Refit the shoe and the grid, then check every joint for drips while the water runs.

Never force a rod hard against a plastic bend. Plastic cracks, and a cracked bend leaks out of sight behind the pipe, which is a worse fault than the one you were clearing. If the rod stops dead and will not shift the plug, stop there.

When it is a job for access at height

A plug in the outlet, or in the offset bend that takes the pipe from the gutter back to the wall, cannot be reached from the ground. It needs access at eaves height. A ladder rested on a gutter loads the one part of the roofline that is not built for weight, so we work from a tower, scaffold or a ladder with a stand-off, never leaning on the gutter itself. If heights are not for you, ask for a visit instead of climbing.

While we are up there, we clear the outlet by hand, look along the run for a dropped joint, and check the bracket nearest the outlet. Brett Martin advises a fall of 1 mm for every 600 mm towards the outlet, and a sagging run holds leaves back at the very point where they choke the pipe, so re-setting it is part of the same visit. Our answer on why gutters overflow in rain goes into the fall.

If the clearing leaves the pipe running but the gutter still spills, the outlet or the fall is the next thing to look at.

When the pipe itself is the problem

Some pipes cannot be cleared back into good order. Signs that point to replacing a length:

a split down the back of the pipe, felt by hand rather than seen
a pipe that has pulled away from its brackets and leans off the wall
a bend cracked by a rod, or by cold weather that froze water inside
a joint that drips after it has been refitted with a new seal

A single damaged length is cut out and a matching one fitted, with new clips to hold it to the wall. A pipe that has failed in several places, on a run of ageing gutter, belongs in a wider job. Our hub page on gutters, soffits and fascias shows how that is judged.

On an older house, a heavy, hard grey downpipe may be asbestos cement. HSE names rainwater goods among the asbestos cement products whose careful, unbroken removal counts as non-licensed work, so we take such a pipe down whole and never hammer it clear. Any broken pieces are bagged and handled as asbestos waste, which has its own disposal route, and the pipe is replaced with a plastic or aluminium length that matches the rest of the run.