The roller cassette inside a sliding patio door is one of the cheapest things in the property and one of the most cost-sensitive to replace. A pair of OEM rollers costs us less than thirty pounds; the labour to fit them costs you closer to two hundred. So it pays — for both of us — to be honest about which problems actually need a new cassette, and which can be lubricated away for another year or two.
The three failure modes
1. The dry roller
The bearings inside the cassette are sealed but not impervious. After a few thousand cycles in a London garden — wind, rain, urban grit — the lubricant inside thins and the bearing turns chattery. The roller still rotates, the door still slides, but the action feels less smooth than it did. This is the case where lubrication is genuinely useful. A dab of PTFE grease on the bearing race extends the life of the cassette by twelve to eighteen months. Pure silicone spray will help for two to three months; lithium grease for nine to twelve.
2. The pitted roller
Once the lubricant has thinned and the bearing has begun to grind, microscopic pits start to form on the inner race. From the outside, you cannot see this — but you can feel it. The roller wheel becomes slightly out-of-round, and the door develops a faint vibration as it slides. Grease will not save a pitted roller; replace it. If you grease over a pitted bearing, you may delay the symptoms for a few weeks, but the metal-on-metal damage continues. By the time the door fails again you will have eaten through the rest of the bearing geometry and the wheel will sit in the cassette at an angle, scoring the track.
3. The seized roller
The endgame. The bearing locks, the wheel stops turning, and the door is dragged across the track on its outer rim. This is the failure mode that bends tracks and ruins lift mechanisms. By the time you get here, you usually need not just rollers but track repair too — at which point a complete sliding-mechanism overhaul is the cheaper outcome than the piecemeal alternative. If a roller has seized, take the door out of service until we attend. Continuing to use it costs more than it saves.
Field test: how to tell which one you have
Take the door fully open. Lift it slightly with both hands. Then test three things:
- Vertical play. If you can lift the door more than a millimetre, the bearing is past its prime — replace.
- Wheel rotation. Get a finger to the visible part of the roller and try to spin it. Smooth = healthy; gritty = pitted; locked = seized.
- Sound profile. Slide the door slowly. A whisper is fine. A consistent low hum is a dry bearing — try grease. A rattle that changes pitch as the door moves is a pitted bearing — replace. A scrape is a seized bearing — stop using the door.
What we charge for the swap
Most patio sliders take a roller pair, supplied and fitted, in the £215–£295 range. Bifolds with multiple rollers are slightly more — usually £80–£140 per leaf. Wardrobes with mirror panels are a different cassette type entirely; expect £130–£180 per door. Track repair is separate, and we'll only quote it if the track itself has been worn.
The honest answer to "do I need new rollers?" is "almost certainly not yet, but probably soon". Run the lift-and-lift test, listen to the slide, and you'll usually know before we walk in.
Booking the replacement
Drop us a paragraph and a photo of the bottom track at [email protected], or use the contact form. Our sliding door fix service notes have the parts and pricing in more detail.