How do you unblock a downpipe?

A downpipe can block in three places, and each needs a different fix. The outlet at the top, where the gutter narrows into the pipe, is the most likely spot because leaves and moss crumbs gather there first. The middle of the pipe can clog where a joint or offset (a bend that steps the pipe round a bay or an eaves overhang) catches debris. The base of the pipe can fail where it meets the drain.

Watch the system in rain, or run a hose into the gutter. If the gutter fills and water barely trickles from the bottom, the top or middle is blocked. If water pours from the gutter end but backs up in the pipe or bubbles at the foot, suspect the drain. A pipe that overflows only at one joint may have a split rather than a blockage, which our answer on downpipe repair covers.

Most blocked pipes are cleared at the gutter. A roofer reaches the outlet from a tower, a scaffold or a properly footed ladder, wearing gloves, and lifts out the wet mass of leaves, moss and silt by hand into a bucket. Scooping it into the pipe only moves the problem lower down. Once the outlet is clear, the gutter is flushed with clean water so that the bit of grit left behind does not start a new plug.

A gutter guard or a balloon-shaped outlet cage can stop leaves entering, but both need checking now and then, and neither suits every system. If you want to compare options, ask which guard suits your gutter before buying one, because a poor fit traps leaves on top and makes more work. The wider job of clearing the whole run is a separate visit, and it is worth doing while the access is up, since the debris that blocked the pipe came from somewhere along the gutter.

When the outlet is clear and the pipe still will not drain, the plug is inside. Push a flexible drain rod or a length of stiff but bendy hose gently down from the top, turning it as it goes, and follow with a strong flow of water. Working from the top lets the water carry the debris out of the bottom, which is the way the pipe is meant to flow. Rodding up from the base tends to pack the blockage tighter.

Go gently with old pipework. Cast iron can crack at the sockets if it is struck, and elderly plastic goes brittle in the sun, so a rough shove can turn a blocked pipe into a split one. If a pipe is old, painted shut at the joints or crumbling at the collars, the sound approach is to stop and have it looked at. Cast iron in particular can often be repaired rather than replaced, but only if it is handled with care from the first moment, and a roofer can tell by looking at the sockets how much strain the pipe will take.

At ground level the downpipe usually ends in a shoe, a short angled piece, over a gully or open drain grating, or connects straight into an underground pipe. If water gathers around the foot of the pipe, or the gully is full of silt and leaves, the pipe may be doing its job and the drain is the part that is blocked. A gully can often be cleared by scooping out the silt with a gloved hand or a small trowel and flushing with a hose, then lifting the grating back square so it sits flush with the paving.

If the water still does not drain after that, the underground pipe is blocked, and it is a job for a drainage firm rather than a roofer. Water sitting against a wall for a long time can also soak the brick and cause damp, so do not leave it, and keep any pooling away from airbricks and door thresholds. Our answer on blocked gutters and damp shows how a trapped flow shows up inside the house.

A downpipe that clogs again and again is telling you something. Overhanging branches, a roof covered in moss and a gutter that holds water all feed the outlet, so the cure is upstream. Cut back what you can, have moss taken off the roof so that it stops shedding into the run, and make sure the gutter drains cleanly towards the outlet. A short check after the first autumn storms is worth the effort, because that is when the year's leaves arrive together.

If you cannot reach the gutter safely, do not improvise. A gutter vacuum works from the ground on many houses, and for the rest we use proper access. The guttering, soffits and fascias page lists the work we do. Once the survey is done, you receive a single total price in writing, with pictures of whatever was blocking the pipe so the explanation matches what you can see.