Three out of every ten phone calls we take in a given week begin with the same sentence: "the patio door has stopped sliding". By the time the homeowner has called us, they have usually tried four things — pushing harder, spraying lubricant, tightening any visible screw, and taking a roller out and putting it back. None of those work for the underlying cause. Below are the six failure patterns we see, ordered by how common they are. If you can rule out the top three before calling, you'll get a quicker quote and a better booking slot.
1. Worn roller bearings
The most frequent culprit by a comfortable margin. The bearings inside the roller cassette go from glassy to gritty to seized, usually over the course of a year. The classic test: open the door fully, lift it slightly with both hands. If you can feel any vertical play at all, the bearings are on their way out. Replace them in pairs — never just the noisy one — because the geometry of the door depends on identical wear on both sides. We carry Roto, GU, Mila and Schueco cassettes in van stock.
2. Track deformation from a single point of impact
Aluminium tracks are softer than people imagine. A dropped flowerpot, a misaligned cleaning trolley, even a heavy garden chair can deflect the track inwards. Once that happens, no roller will run cleanly across that section. Look along the track in raking light — a millimetre of bow is enough to cause a slider to stick. Mild bowing can be straightened with a hydraulic dressing tool; severe bending needs a section cut in.
3. Compacted debris in the lower channel
This one is a free fix. A combination of leaf litter, hair, sand and dried-out lubricant collects under the rollers and acts as a small mountain that the door has to drag itself over. Most homeowners hoover the channel; few clean it deeply enough. We use a stiff brush, a vacuum, and a clean rag with a drop of WD-40 to dissolve the residue. About one in twenty visits ends here, with no parts replaced.
4. Failed brush or rubber seals
The brush seal at the top and the rubber seal at the bottom are not load-bearing — but if they collapse and start dragging, the door behaves as though the rollers are at fault. A glance from above will tell you whether the brush is matted or twisted. A new brush kit takes ten minutes to fit and is the cheapest part of any sliding-door overhaul.
5. Out-of-square frame
This one's harder to spot at home. If the building has settled (most London terraces have), the frame may have shifted by a few millimetres at the top corner, putting the door into a parallelogram rather than a rectangle. A measure across both diagonals usually reveals it: anything over 4mm of difference and the door cannot run cleanly. The fix is shim-based — we adjust the rollers to compensate, but a substantial frame distortion may need carpentry beyond what we cover.
6. Locking mechanism partially engaged
Last on the list because it's the easiest thing to rule out — yet we still see it once a month. A multipoint lock that has partly engaged will hold the door in place even when the handle looks fully down. Lift the handle fully, then push the door firmly to its lock-end, then drop the handle again. If the door now slides freely, the lock-cam is dragging on the keep — book a fitter, but the urgency drops.
Sliding hardware is sensitive. The right fix is rarely the obvious one. Lubricant, longer screws and brute force will buy you a few weeks. Diagnosis is the difference between a thirty-pound roller swap and a six-hundred-pound replacement door.
Before you book
Three photos make our job easier: one of the open door from the inside, one of the bottom track from the outside, and one of the lock face when the door is closed. A short video of the door in action is even better. Send them to [email protected] and we will tell you, almost always inside two hours, which of the six it is and what it costs to fix.
Open the contact form if you'd like to brief us properly, or read our sliding door & wardrobe fix service notes for the parts and the pricing.