How do I replace the rollers on a sliding patio door?

Rollers wear out, and on a door that has run dirty for years they wear out fast. Replacing them is not technically difficult but it involves handling a very large, very heavy piece of glass, which is where all the risk in this job sits. Be honest about whether you have two capable people and somewhere flat and clear to put the sash down.

Safety

What you'll need

• A second person, minimum
• Glass suction lifters (optional)
• A clean flat area with blankets or foam to lay the sash on
• Screwdrivers and hex keys
• Replacement carriages, matched
• A vacuum and cleaning kit for the track

Step by step

1. Identify the door type first.Some sliding doors lift out inwards; some have a removable interlock or a retaining strip in the head track; a few are designed not to come out at all without dismantling the frame. Look for screws in the head track and along the interlocking stile before applying any force.
2. Photograph everything.The track, the head channel, any anti-lift blocks, the position of the sash in the closed position, and the carriages once they are visible. You will want these when it goes back.
3. Lower the sash fully.Wind both roller adjusters all the way down so the sash sits as low as it can. This gives the maximum clearance at the head when you lift it out.
4. Remove any anti-lift blocks.Most sliding doors have small blocks or plates in the head track that stop the sash being lifted out — they are a security feature. They are normally screwed and removable from inside. Note exactly where they were.
5. Lift and swing the sash out.Slide the sash to the middle of its travel. Two people, one at each end, lift it straight up into the head track until the bottom clears the track rib, then swing the bottom inwards and lower it. Move slowly and talk to each other.
6. Lay it down properly.Flat, on blankets or foam, glass side up, in a place nobody will walk into. Do not lean it against a wall on a hard floor — the frame corner will slip.
7. Remove the carriages.They are held into pockets in the bottom rail by one or two screws each, usually from the inside face or the underside. Take one out first and keep it as a reference while you deal with the other.
8. Match the replacement carefully.Wheel diameter, wheel width, whether the wheel is nylon or steel, the overall carriage body length and depth, the fixing hole positions and the adjuster type. Take the old carriage to a specialist supplier or photograph it with a rule alongside.
9. Clean the track properly while the sash is out.This is the only time you will ever have proper access. Vacuum, scrub, clear the drainage slots at the outer edge, dress any burrs on the track rib, and consider a stainless capping strip if the track is worn.
10. Fit the new carriages and set them mid-range.Wind the adjusters to roughly the middle of their travel before refitting, so there is adjustment available in both directions once the sash is back in.
11. Refit the sash, reversing the removal.Two people, into the head track first, then swing the bottom out and lower onto the track. Check the wheels have actually landed on the rib rather than beside it before letting go.
12. Refit the anti-lift blocks and adjust.The blocks go back exactly where they were — a sliding door without them can be lifted out from outside. Then set the height and squareness with the adjusters and check the lock engagement.

Common mistakes

• Attempting it single-handed — This is the injury and the broken-glass job. A large sealed unit in an aluminium or uPVC frame is heavier and more awkward than it looks and there is no way to recover it once it starts to go.
• Not refitting the anti-lift blocks — They are the reason the door cannot be lifted out from the garden. Leaving them out turns a secure door into an unsecured one.
• Buying rollers on the wheel size alone — Carriage bodies vary in length, depth and fixing positions between makes, and a carriage that will not seat in the pocket cannot carry the sash.

Questions people ask