How Do You Unblock a Downpipe?

Find where the blockage is

Before you poke a rod into a pipe, work out where the water is stopping. Wait for rain, or pour a bucket of water into the gutter near the outlet, and watch. If water backs up in the gutter and pours over the front edge, the problem is at or above the outlet. If water goes into the pipe but spills from a joint halfway down, the blockage is inside the pipe below that joint. If water runs down and then comes back up at the foot, the trouble is the shoe or the drain at the bottom.

Listen as well. A gurgle, or the absence of any flow sound, tells you the pipe is full. Tap down the length of the pipe; a dull sound where the rest rings hollow shows a plug of debris. A pipe that is bulging, leaning or cracked at a joint may have frozen and split in winter, and a split pipe cannot be saved by clearing it.

How to clear it safely

Most blockages are soft and loose, so the gentlest method is best. Work from the outlet down:

• Lift out leaves and silt from the gutter near the outlet by hand, in gloves, using a small trowel or a gutter scoop. Bag the waste.
• Push a drain rod, a length of stiff garden hose or a plumber's snake down the pipe to break up the plug. Do not force it, since a rod pushed hard can split a joint or push the debris into a bend.
• Flush with a hose from the top, with the water running until it comes out cleanly at the bottom.
• If the pipe is still blocked, unclip it from the brackets, take it down and clear it on the ground by tapping, rodding and rinsing.

Never lean off a ladder to reach an outlet, and do not use a power washer on the gutters, because the pressure can force water behind the fascia. If the gutter is above first-floor height, use a tower or call someone with access, since clearing from the ground with a long-reach tool can only do so much. Our gutter maintenance guide sets out what is safe to do yourself.

Frozen pipes deserve a mention. In a hard frost, water standing in a blocked pipe turns to ice and swells, and the pipe can split along its length or push a joint apart. The damage often shows only at the thaw, when water pours from the crack. If you suspect ice, wait for it to melt before rodding, and do not pour boiling water over a plastic pipe, which can soften and distort it. Warm tap water is enough.

The shoe, the gully and the drain

At the bottom, the downpipe ends in a shoe, which is an angled outlet that throws water onto a gully or a drain. That is where silt and grit collect, and in a clay drain or an old gully the water can stand and form a plug of mud and leaves. Lift the grid, scoop out the sludge and flush the gully. If the water rises and does not go away, the drain run is blocked and the problem lies in the drainage, not the gutter. A drain clearance service or a rodding visit is the answer there, and not a roofer.

Where the downpipe feeds a soakaway or a water butt, check those too. A full butt with a blocked overflow sends water straight back up the pipe.

When it keeps blocking

A pipe that clogs every autumn tells you something. The gutter above may be full of moss and roof grit, so it feeds the outlet with debris each time it rains. The outlet may be too small for the roof area, or the pipe may have a bend where silt lodges. Trees overhanging the roof will always add leaves. Gutter guards help in some cases, and whether gutter guards are worth it explains when, though they do not cure a pipe that is crushed or badly aligned.

If clearing gives only short relief, the cause is likely to be an overflowing run; read why gutters overflow to check the causes. For a routine, see how often gutters should be cleaned.

Our free survey looks at the whole run, from the outlet to the drain, photographs what we find and tells you if a clear-out will do or if parts need replacing. You can read about the service on the guttering, soffits and fascias page.