How do I clear a blocked downpipe?

Clearing a downpipe or gully that has blocked, and how to tell where the blockage actually is.

Difficulty: intermediate
Time: 1 hr
Read: 2 min
Safety: caution

Short answer

Water overflowing at the gutter with a dry downpipe means the blockage is at the top. Water backing up at the bottom means it is in the gully. Clear the top by hand, the pipe with a hose or drain rod from the bottom, and the gully by hand with gloves.

A blocked downpipe shows itself as water pouring over the gutter or pooling at the base of the wall, and that overflowing water is what causes penetrating damp. Locating the blockage before working is what stops you clearing the wrong end.

Safety

Working at height on gutters carries real risk. Never work from a ladder on soft or sloping ground, never overreach, and treat two-storey work as a job for someone with the right equipment. Clearing the gully at ground level is safe and is often where the blockage actually is.

What you'll need

Gloves
Hose
Drain rods or a length of flexible cable
Bucket
Ladder with stabiliser (optional)

Step by step

Watch what happens during heavy rain, or run a hose into the gutter.Overflow at the gutter means the top is blocked. Water backing up at the bottom means the gully is.
Clear the gully at the bottom first — it is safe and is often the cause.Gloves on, lift the grate, and pull out the leaves and silt. Bucket ready.
Run a hose into the downpipe from the top and see whether it flows freely.If it backs up, the blockage is in the pipe itself.
Feed drain rods or a flexible cable up from the bottom, or down from the top.Upwards from the bottom is usually easier and safer, and gravity brings the debris down.
For a blockage at a swan neck or a bend, dismantle that section.Most plastic downpipes push-fit or have simple clips and come apart easily.
Flush the whole run with a hose once clear.This is the test. Watch the outlet at the bottom.
Fit a leaf guard at the gutter outlet.A simple wire balloon in the outlet stops most of what causes downpipe blockages.
Check that the gully drains freely afterwards.A clear downpipe discharging into a blocked gully still floods the base of the wall.

Tips

Autumn after leaf fall and again in spring is the right rhythm for most houses with trees nearby.
Overflowing gutters in winter are a leading cause of penetrating damp, so this is worth doing before the wet months.
Ground-level gutter vacuums and camera poles remove the ladder risk entirely and are worth hiring for a day.

Common mistakes

Clearing the gutter but not the downpipe or gully — The blockage is often below the gutter and the water still backs up.
Leaning a ladder against the gutter — Plastic gutters distort or break under load and the ladder slips.
Ignoring an overflow because it only happens in heavy rain — That is exactly when it causes the most water damage to the wall.

Questions people ask

How do I know if the blockage is in the gutter or the downpipe?

Run a hose into the gutter. If it overflows at the top, the gutter or the outlet is blocked. If it drains from the gutter but backs up at the bottom, the downpipe or gully is.

How often should downpipes be checked?

Twice a year — after autumn leaf fall and again in spring. Checking during actual rain from a window shows overflow points that are invisible on a dry day.