Leaking Gutter Joints: Clean, Reseal or Replace?

Step one: rule out a blockage first

Before assuming a joint has failed, check whether the gutter either side of the leak is clear. A blockage downstream of a joint can force water to back up and find its way out through even a perfectly sound union seal under enough pressure, mimicking the appearance of a joint failure. This is genuinely the most common false alarm we see on leaking joint call-outs.

A quick way to test: if the dripping stops or reduces noticeably after the gutter's been cleared and flushed, the joint itself may well be fine, and the blockage was the actual cause all along.

Step two: a failed seal, usually fixable with a reseal

If the joint still drips with a clear, unblocked gutter either side, the union seal itself (a rubber or silicone gasket inside the joint) has likely perished, shrunk or come loose, which is a normal age-related failure after years of UV exposure and weather cycling. This is usually a straightforward and inexpensive fix: the joint is cleaned, the old sealant removed, and a fresh seal or sealant applied.

For cast iron or older metal guttering, joints are sometimes sealed with a mastic-type compound rather than a rubber gasket, which also perishes over time and can be similarly resealed rather than requiring the whole joint to be replaced.

Step three: when a joint needs full replacement

If a joint is cracked, has visible gaps that won't close even when correctly seated, or the gutter sections either side of it have moved out of alignment (often from bracket sag or impact damage), resealing won't hold reliably and the joint union itself needs replacing. This is a slightly bigger job but still generally modest in cost for a single joint, particularly compared with the water damage a persistent leak can cause if it's left.

On very old guttering systems where multiple joints are failing at once, it's worth having an honest conversation about whether individual joint repairs are the best use of money versus a fuller guttering renewal, especially if the system is nearing the end of its expected life anyway.

A useful rule of thumb: if you've already resealed the same joint more than once and it keeps failing within a year or two, that's usually a sign the union itself needs replacing rather than another reseal being the answer.