Why Will My uPVC Door Not Lock in Hot Weather?

Because heat has expanded the door leaf and the steel reinforcement inside it, so the locking points no longer line up with the keeps in the frame. The door has not broken. It has grown by a small amount, and a multipoint lock needs the hooks and rollers to meet their keeps within a very tight tolerance, so a fraction of a millimetre in the wrong place is enough to stop the handle lifting.

The important thing is what you do in the next thirty seconds, because this is one of the few faults where the customer's instinctive reaction is what causes the actual damage. Do not force the handle upwards. A door that will not lock on a hot day is usually fine until somebody puts their shoulder into the handle. Forcing it against resistance snaps the gearbox inside the lock, and that turns a problem which would have solved itself by evening into a mechanism that has to be replaced.

Why does heat do this to a uPVC door and not to a timber one?

Different materials, moving in different ways and at different rates.

Timber swells with moisture, which is why a timber door sticks in damp weather and eases in dry weather. uPVC does the opposite. It responds to temperature rather than humidity, expanding as it warms and contracting as it cools. Inside most uPVC doors there is also a galvanised steel reinforcement running through the profile, and that expands too, at its own rate.

So on a hot day you have a door leaf that is very slightly larger than it was, sitting in a frame that has also moved, with a steel core adding its own movement. Individually each change is tiny. Together they are enough to shift the hooks out of alignment with their keeps.

• Dark doors are affected far more than pale ones. Anthracite, black and dark blue absorb considerably more heat than white or cream, and the difference in surface temperature on a south facing elevation is substantial.
• South and west facing doors are the usual ones. They take the most direct sun, so a north facing door doing the same thing points to a different cause, which is a useful diagnostic in itself.
• A door with no porch or canopy is more exposed than one sitting back in shade for part of the day.
• The problem usually appears in the afternoon and has gone by the following morning, which is the clearest sign that heat rather than a fault is behind it.

What should you do at the time?

Take the pressure off and let it cool. That is genuinely the whole answer in the moment.

• Lift the handle gently, and stop the instant you feel resistance. If it will not go, it will not go, and the gearbox is the part that pays for persuading it.
• Pull the door firmly towards you by the handle while lifting. Very often the hooks are only marginally out and holding the leaf tight against the frame is enough to let them find their keeps.
• Cool the door down. Shade helps, and running cold water over the outer face brings the temperature down quickly. It looks like an odd thing to do to a front door and it works.
• Wait for the evening if you can. As the leaf cools it returns to size and the lock behaves normally again.
• If you must leave the house, do not leave the door pulled to. A door that will not lock is not secure, so give it time to cool or call us rather than leaving it on the latch.

Is it definitely the heat, or something else?

Worth checking, because two other faults look almost identical and one of them gets worse if ignored.

• A dropped door behaves the same way but does it all year round. If the trouble started gradually and happens in all weather, the leaf has sagged on its hinges rather than expanded.
• Worn keeps produce the same symptom on an older door. The rollers and hooks wear a groove in the keeps over years, and eventually the engagement becomes marginal in any temperature.
• A failing gearbox feels different. The handle goes up without much resistance but nothing engages, or it engages and will not release. That is mechanical and it is not going to improve.
• A swollen threshold or a dropped cill occasionally lifts the bottom of the door enough to misalign the lowest hook, particularly on doors with a low threshold.

The tell for heat expansion is that the door works perfectly when it is cool. If it is stiff first thing on a cold morning too, the heat is not the cause and something needs adjusting.

Can you not just adjust the hinges and be done with it?

You can adjust them, and that is the proper fix. The timing is what matters, and this is where a lot of well-meant call-outs go wrong.

Adjusting a door once it has cooled works better than adjusting it while it is hot and sticking, because a door set up at its expanded size is being given clearance it does not need for most of the year. Come the winter, the same door is now loose in the frame, the compression against the weather seal has gone, and the customer has a draught and a rattle where they used to have a door that stuck on three afternoons a year. We would rather come back on a cool morning and set it properly once.

The adjustment itself is straightforward on most modern hinges. They allow lateral movement to bring the leaf towards or away from the keeps, height adjustment to lift a dropped door, and compression adjustment to control how hard the leaf pulls against the seal. What we are aiming for is enough clearance that the door still has somewhere to go on the hottest day, without giving away the compression that keeps it weathertight and draught free the rest of the year. That balance is the actual skill in it.

Does it mean the door was badly made or badly fitted?

Not necessarily, and it is worth being fair about this.

All uPVC expands. A door fitted with proper clearance will cope with normal heat without complaint, and one fitted tight will not, so installation is often a factor. But a door that has behaved for years and only recently started sticking has usually not changed. Either the weather has been more extreme than it used to be, or the hinges have crept, or the keeps have worn.

Where the fitting genuinely is the problem, it tends to show in the first year rather than the tenth, and it usually comes with other signs such as uneven gaps down the closing edge or a leaf that is visibly out of square in the frame.

Would a different door solve it permanently?

Sometimes, and it depends on what is actually failing.

A composite door has a solid core rather than a hollow reinforced profile, so it behaves differently in heat, though no external door is completely immune to movement. If your existing door is an older uPVC one that has dropped, has worn keeps and sticks every warm afternoon, you are dealing with three things at once and replacement starts to make more sense than a rolling series of adjustments.

That said, we would rather adjust a sound door than sell you a new one. If the leaf is straight, the frame is square and the hardware works when the door is cool, this is a maintenance visit and not a reason to replace anything. The wider signs that something has genuinely reached the end of its life apply to doors as much as windows, and sticking on hot days on its own is not one of them.

It is also worth knowing how long a uPVC unit should realistically last before spending on repairs, because there is a point where adjusting an old door is postponing a decision rather than solving anything.

So, what should you do about a uPVC door that will not lock in the heat?

In the moment, stop lifting. Pull the door firmly towards you and try the handle gently, cool the leaf down with shade or water, and wait for the temperature to drop if you possibly can. Forcing the handle is the one action that converts an inconvenience into a bill.

Once the weather has settled, get the hinges adjusted properly on a cool day rather than a hot one, so the door keeps its weather seal through the winter as well as its clearance through the summer. If it sticks when it is cold too, it is not the heat and something else needs looking at.

Our team has over 30 years of experience adjusting and fitting doors across Surrey, and this is a small job rather than a big one. If yours is doing it, get in touch and we will tell you honestly whether it needs adjusting or replacing.