The short answer
If your uPVC door won't lock, the cause is almost always one of five things: the door has dropped, the keeps are out of line, the gearbox inside the lock has worn out, the cylinder is failing, or the handle spring has broken. Most of these can be repaired the same day without replacing the door.
The good news is that you can usually work out which one it is in a few minutes. The table below shows what each fault feels like.
Why won't my uPVC door lock? The five common causes
| What you notice | Likely cause | Usual fix |
|---|---|---|
| Handle is stiff to lift, worse in hot or cold weather | Door has dropped or swollen, so the hooks and rollers do not meet the keeps | Adjust hinges and keeps |
| Handle lifts only when you push or pull the door hard | Keeps out of line with the locking points | Realign or move the keeps |
| Handle lifts but nothing moves, or it feels loose and grinds | Worn or broken gearbox in the multipoint lock | Replace the gearbox or the whole lock strip |
| Key is stiff, turns only part way or will not turn | Worn or damaged cylinder | Replace with an anti-snap cylinder |
| Handle droops and does not spring back | Broken handle spring or cassette | Replace the handle set |
What you can safely check yourself
- Look at the gap. Close the door and look at the gap around the frame. If it is wider at the top on the handle side, the door has probably dropped.
- Check the keeps. Look for shiny rub marks on the keeps on the frame. Marks on one edge mean the locking points are catching.
- Test with the door open. With the door open, lift the handle and turn the key. If everything moves smoothly, the lock is fine and the problem is alignment. If it is still stiff, the lock itself is worn.
- Do not force it. Forcing a stiff handle is the most common way a gearbox breaks. If it will not lift, stop.
When you need a locksmith
Call a locksmith if the handle feels loose or grinds, if the key will not turn even with the door open, or if the door is stuck locked. These faults are inside the lock case and need the right parts. A multipoint lock is a lock with several hooks, rollers or bolts along the door edge, all worked by one handle. The gearbox is the central part behind the handle that drives them. When it wears, the whole door stops locking.
A trained locksmith can often replace just the gearbox, which costs less than a full lock strip. If the cylinder is old, it is worth changing it at the same time for a TS007 3-star or Sold Secure Diamond anti-snap cylinder.
How much does a uPVC door lock repair cost?
Checkatrade's May 2026 cost guide puts a standard uPVC lock change at about £100 to £150, and an anti-snap uPVC lock at about £150. Gearbox repairs and alignment jobs often fall at or below this range, depending on the parts. We always give you a written price before any work starts.
How to stop it happening again
- Lift the handle gently and never force it.
- Spray a light lubricant into the locking points twice a year.
- Get the door adjusted as soon as it starts to feel stiff, before the gearbox wears.
Related service: uPVC door lock repair in London.
A few common questions
Why is my uPVC door handle stiff to lift?expand_more
A stiff handle usually means the door has dropped or swollen, so the locking points no longer line up with the keeps on the frame. Adjusting the hinges and keeps often fixes it. If the handle is still stiff with the door open, the gearbox inside the lock is likely worn and needs replacing.
Can I fix a uPVC door that won't lock myself?expand_more
You can check the gap, look for rub marks on the keeps and test the handle with the door open. Small hinge adjustments are possible with the right tools. Anything inside the lock case, such as the gearbox or cylinder, is best left to a locksmith, because forcing parts can break them.
How much does it cost to repair a uPVC door lock?expand_more
Checkatrade's May 2026 guide puts a standard uPVC lock change at about £100 to £150, and an anti-snap lock at about £150. Simple alignment or gearbox jobs can cost less. A good locksmith will give you a written price before starting, so you know the cost upfront.
What is a gearbox in a uPVC door?expand_more
The gearbox is the central part of a multipoint lock, fitted behind the handle. When you lift the handle, the gearbox drives the hooks, rollers and bolts along the edge of the door. When it wears out, the handle may feel loose or grind and the door will not lock.
Should I replace the cylinder when my uPVC lock is repaired?expand_more
If the cylinder is old or is not anti-snap rated, yes. Many older cylinders can be snapped to open the door. A TS007 3-star or Sold Secure Diamond cylinder resists this attack and is quick to fit while the locksmith is already working on the door.