Why your downpipe keeps overflowing and what fixes it
When it rains hard and water spills over the gutter by the downpipe, or sprays from a joint halfway down, something is stopping the water getting away. It is almost never the downpipe being too small. It is a block, a break or a connection that is not doing its job.
This post goes through the causes in the order we find them, starting with the commonest.
A blocked outlet at the top
Most overflows start here. The outlet is the hole in the bottom of the gutter that the downpipe hangs from. Leaves, moss and silt gather in the gutter and wash toward the outlet, where they pack in like a plug.
If water pours over the front of the gutter right next to the downpipe, this is the likely cause. A proper gutter clean that clears the outlet and checks the pipe below it is the fix. It costs between £90 and £250 for most houses, depending on size, height and how much is in there.
A block further down the pipe
Sometimes the outlet is clear but the pipe is not. Debris that gets past the outlet can wedge at a bend or a joint. You will notice the gutter filling slowly, then overflowing, while water trickles from the pipe.
A gutter vacuum and reach poles can clear the pipe from the top. Flushing a hose through from above shows whether it runs freely, but do not push things down the pipe, because you can jam it further.
Leaks at joints and brackets
If water comes out of the pipe part-way down, look for a split, a gap between lengths or a joint that has slipped. Plastic pipes can crack, and old cast-iron ones can open at joints.
- A weeping joint with staining beneath it can often be resealed or refitted.
- A cracked pipe needs that length replacing.
- A pipe that has pulled away from the wall needs its brackets refixing.
Our page on downpipe installation and replacement explains how we fit and swap them.
A blocked drain at the bottom
Water that cannot leave the foot of the pipe backs up the whole thing. Look at where the downpipe ends. If it runs into a gully or a drain and that is full of silt, leaves or standing water, the pipe will overflow even though it is clear.
Clearing a gully is a drainage job and not part of guttering, so if you suspect the drain, it is worth having that looked at. We will tell you what we find at the base of the pipe when we are there.
Gutters that have lost their fall
A gutter has to slope very slightly toward the outlet. If brackets have dropped or the run has sagged, water sits in the low spot and tips over when it fills. You will see this as standing water in the gutter after rain, or a regular overflow at the same place.
Re-fixing the brackets, or relaying the gutter at the right slope, solves it. Cleaning alone will not.
Too much roof for one pipe
A big roof draining to a single downpipe can overwhelm it in a downpour. Extensions are a common case: more roof area has been added, but the gutter still drains to the old outlet. In that case a second outlet or a different layout can help.
This is rarer than a blockage, so rule the blockage out first.
Will a guard stop it?
Sometimes. If leaves from a tree are the problem, a guard can reduce what reaches the outlet. It will not help with moss, joints or a lost fall. We cover the pros and cons in are gutter guards worth it.
What not to do
- Do not lean a ladder on the gutter. Plastic gutters crack under it, and falls from ladders are a real danger.
- Do not poke a stick or wire down the pipe. It can wedge debris tighter or crack the pipe.
- Do not ignore a repeat overflow. If it happens in every heavy shower, the water is running down your wall each time.
- Do not seal a leaking joint with whatever is in the garage. Sealant on a dirty joint does not hold.
If the pipe itself is old, cracked or the wrong size for the roof, replacing it is often tidier than repeated fixes. Our gutter replacement page covers the wider job when the whole run is tired.
A quick check you can do from the ground
- Watch the downpipe in heavy rain and note exactly where the water escapes.
- Look for water pouring over the top, or leaking from a joint.
- Check the drain at the bottom.
- Take photos and ring us, or send them on WhatsApp.
If you want to try clearing low gutters yourself first, our DIY gutter cleaning guide covers it safely.