Why Does Strimmer Line Keep Breaking? Causes and Fixes

Strimmer line snaps constantly for three main reasons: it has dried out in storage, you are cutting against hard surfaces with the wrong part of the head, or the line is too thin or too cheap for the job. Nearly every case comes down to one of those, and all three are fixable in a few minutes. Below is how to work out which one is happening to you.

1. The line has dried out

This is the most common cause and the one nobody suspects. Nylon line is hygroscopic: it absorbs and loses moisture from the air. A spool that has sat in a hot shed or a cold garage over winter goes brittle. It looks fine, but it shatters the moment it touches a fence post instead of flexing.

The test is simple. Pull a length off the spool and bend it back on itself into a tight loop. Healthy line bends and springs back. Dried line makes a faint crack and snaps, or leaves a white stress mark at the fold.

The fix is to rehydrate it: drop the spool in a bucket of water for 24 hours, shake it off and let the surface dry before fitting. It will not save line that is years old, but it makes a real difference to line that has had one bad winter. After that, store spare spools in a sealed bag or airtight tub with a splash of water in the bottom, kept indoors rather than in the shed.

2. You are cutting with the wrong part of the head

Most people push the head straight into the grass so the line is buried up to the eyelet. That puts the thick, slow-moving section near the spool to work while the fast, efficient tip spins in fresh air.

Line cuts by speed, not force. Only the outer 25mm or so has enough tip speed to slice cleanly. Bury the whole length in dense growth and you are bludgeoning it, which loads the line, overheats it and rips it off at the eyelet. Sweep the head side to side and take shallow bites instead, especially in long or wet grass. It feels slower for the first minute, then it is not, because you stop halting every ninety seconds to feed more line.

3. The line is too thin for what you are cutting

Line diameter should match the job. As a rough guide:

• 1.2mm to 1.6mm: light lawn edging and soft grass only. Put it near brambles and it vanishes.
• 2.0mm to 2.4mm: the sensible general purpose range for a domestic garden of grass, nettles and weeds.
• 2.7mm and up: heavy brush and thick stems, and it needs a machine built to take it.

Fitting thicker line than the manual specifies is not the automatic answer either. Oversized line will not feed through the eyelets properly, drags the motor down and drains a cordless battery fast. Check the sticker on the head and stay within the stated range.

4. Line shape and quality matter more than the price tag suggests

Round line is the toughest and most forgiving, which is why it comes as standard. Square, star and twisted profiles cut more aggressively because they have sharp edges, but those same edges are stress points that break sooner against hard surfaces. Around a gravel drive or a brick wall, plain round line lasts considerably longer than a fancy shaped one.

Cheap unbranded line is genuinely worse, too. Poorly extruded nylon has inconsistent thickness and internal voids, and it fails at whichever weak point comes first. Co-polymer or reinforced line costs a little more per metre and takes far more punishment.

5. Hard surfaces are doing the damage

Concrete, brick, kerb edges, fence panels, tree bark and metal posts all destroy line, and so do stones hidden in long grass. When edging along a path, angle the head so the line skims just above the surface rather than grinding into it, and use the guard as a spacer. Around trees and posts, slow right down and use the very tip.

6. Check how the spool is wound

A badly wound spool causes breakages that look mysterious. Wind in the direction of the arrow on the spool, keep the coils tight and neat, and never let two layers cross over each other. Crossed line binds inside the head, so when the machine tries to feed, the line cannot move and tears instead. On a bump feed head, check the spring and the knob as well; a weak spring means the line either will not release or dumps too much at once.

A quick diagnostic order

1. Bend test a length of line. Brittle? Replace or soak it.
2. Feel the eyelets for a groove or burr. Worn? Replace the head.
3. Check the line diameter against the manual.
4. Rewind the spool tightly in the arrowed direction.
5. Change your technique to cut with the outer tip only.

Work through those in order and most persistent breakage problems disappear. If line still snaps within seconds on soft grass with a fresh spool and a new head, the machine is likely spinning the head well outside its designed speed, which is worth raising with the manufacturer while it is under warranty.