The short answer
Most gutter leaks start at a joint. Rubber seals perish with age and sun, sealant dries out and cracks, plastic expands and contracts with temperature, and a sagging run pulls the sections apart. The usual fixes are cleaning and resealing the joint, replacing the union or seal, or adding a bracket close to it. If every joint weeps, the run itself is tired.
Why joints fail
A gutter is made in lengths, and every place where two lengths meet is a joint. In plastic systems a joint is a union bracket with a rubber seal that grips both ends. In metal systems it is a lapped or clipped joint, sealed with a bead of sealant. Water, sun, frost and movement attack these seals constantly.
Age is the commonest cause. A rubber seal hardens, cracks and shrinks over years, and loses the pressure that keeps it watertight. Sealant dries out and splits. Debris can sit in the joint and wear the seal, and a joint that is regularly under water, because the gutter holds a pool, perishes faster.
Thermal movement is the second cause. Plastic expands and shrinks with temperature far more than metal, and a long run lengthens in summer and shortens in winter. A joint with no allowance for that movement is pulled and pushed until it opens. Many unions have a mark showing how far the gutter should be pushed in to leave room for expansion, and joints fitted ignoring it fail early.
Poor support is the third. If brackets are too far apart, or have pulled loose, the gutter sags and the joint is stressed. A joint at the sagging point is where a drip first shows.
Finally, blockages and bad falls make water stand in the gutter, putting pressure on every joint along the run.
Finding the leaking joint
The dripping point is not always the faulty joint. Water can run along the underside of the gutter before it drops, so check a short distance either way. On a dry day, run a hose into the gutter above the suspect area and watch where water escapes.
Look for signs. Streaks on the fascia or wall below a joint, green growth, damp stains, staining on the underside and white or dark marks on the gutter itself all point to a long-running drip. Rust trails on a metal gutter show where it has been wet.
Check what is around the joint. Is the gutter level or sagging? Are brackets present within a short distance on each side? Is the fascia sound? A joint in a gutter that has lost its fall will leak again after resealing, and a bracket loose in rotten timber will not hold.
Inside the joint, look for a split, perished or dislodged seal, a gap where the ends have drawn apart, dirt or old sealant that has failed, and corrosion or cracks in the union.
Do this from a safe position. A joint is often high, and a tower or the right ladder is needed. Do not lean out from a ladder or work in wet weather. Our page on why gutters overflow helps tell a joint leak from an overflow.
Fixes, from reseal to replace
The cure follows the cause. For a joint with a dried seal and sound parts, the repair is to clean it, remove old sealant and dirt, and reseal with a sealant made for gutters, or fit a new rubber seal. The gutter must be dry and the weather suitable for the sealant to cure.
If the union is cracked, corroded or distorted, it is replaced with a new one of the right profile. For plastic, a fresh union with a new seal takes minutes. For metal, a new joint with the correct sealant may be needed, and fatigued sections may be cut out and replaced.
Where the cause is movement or sag, address that too. Add or refix brackets close to the joint, re-hang the run to a proper fall and check the push-in mark for expansion. Brett Martin's guide is a fall of 1 mm for every 600 mm of gutter.
Do not rely on sealant alone to hold a joint together. Sealant fills a gap and does not carry load. A joint pulled apart by a sagging run needs the run supported.
If many joints leak, or the plastic is brittle, repeating repairs along the length will be a poor use of money. At that point replacing the run is the sound answer, as our page on how often guttering needs replacing explains.
What we do and what it costs
We find the leaking joint, check the brackets and falls either side and look at the fascia behind. A photograph of the joint and the surrounding gutter records the fault. Often it is a case of resealing or swapping a union and adding a bracket, a short job.
If the survey shows the run is worn out, we explain why and what replacement would involve, with the evidence on show. We would rather mend a sound gutter than sell a new one, and rather replace a tired one than repeat visits.
Cost follows the work. A reseal or a union is small. MyJobQuote's range for full gutter replacement is around £1,000 to £1,600 (MyJobQuote, Oct 2026), a typical UK figure, so a repair that covers most of a run begins to approach that level. Access, in the form of a ladder, tower or scaffold, can matter as much as the parts.
The figure you receive is a single total in writing, with access and VAT stated. For the wider picture, see what decides the cost of a gutter repair, and the gutters, soffits and fascias hub for the roofline as a whole.
