Why Does My uPVC Door Stick in Hot Weather? The Heat Expansion Problem Explained

Every summer, we receive a surge of calls from homeowners across Leicestershire, Northamptonshire, and Nottinghamshire reporting the same problem: their uPVC door, which worked perfectly throughout winter and spring, has suddenly become difficult to lock, stiff to close, or has developed an annoying draught on one side.

The good news is that the cause is almost always the same — and it is something we can fix.

Why uPVC Expands in Heat

uPVC (unplasticised polyvinyl chloride) is a thermoplastic material, which means it responds to temperature. On a warm summer's day, particularly when a dark-coloured door is exposed to direct sunlight, the surface temperature of a uPVC door can reach 60°C or higher — well above the ambient air temperature.

At those temperatures, uPVC expands measurably. A standard-size uPVC door can expand by several millimetres across its width and height during a hot day. In most cases, this is a normal characteristic of the material, and a properly installed and aligned door is designed to accommodate a degree of thermal movement.

However, when a door is already slightly out of alignment — often because the hinges have worn, the door has dropped, or the frame has settled — even a small amount of heat expansion is enough to push the door into the frame at the wrong angle, causing it to stick, rub, or become impossible to lock.

What "Dropping" Means and Why It Matters

Door dropping is the most common underlying cause of heat-related sticking problems. Over time, the weight of a uPVC or composite door — which can be considerable, particularly for solid composite doors with glass panels — places stress on the hinges. The hinge fixings gradually loosen, and the door begins to drop at the lock side.

When a door drops, the locking bolts on the multi-point lock no longer align precisely with the keeps on the door frame. In cooler weather, this misalignment may be slight enough that the door locks with a firm push and a firm lift of the handle. When the door expands in heat, the tolerances tighten further, and what was manageable becomes impossible.

Signs Your Door Has a Heat Expansion Problem

• You have to push the door firmly into the frame, or lift it slightly, to get it to lock during warm weather
• The door locks easily in winter but becomes stiff or immovable in summer
• There is a visible draught on one edge of the door, particularly the hinge side
• The handle feels unusually stiff to lift, or requires significant effort
• You can see light around the edge of the door on the lock side when it is closed

Why You Should Not Ignore It

Forcing the handle upward to engage the locks when a door is misaligned puts enormous stress on the internal locking gearbox. The gearbox is a mechanical component, and repeated force in a binding situation will eventually cause it to fail completely — either snapping internally so the handle spins freely, or seizing so the door cannot be opened at all from the outside.

Replacing a failed gearbox is more expensive and more disruptive than simply adjusting the door alignment before the gearbox fails. If your door is stiff in summer, addressing it now is always the more cost-effective choice.

How We Fix It

The solution in most cases is a hinge adjustment. Modern uPVC door hinges are engineered to be adjustable in three axes — up/down, in/out, and laterally — using small Allen key adjustments on the hinge body. A properly trained door repair engineer can adjust the hinges to lift the door back into square, realigning the locking bolts with the keeps and restoring smooth, effortless locking even at high temperatures.

In some cases, particularly on older doors where the hinge fixing screws have pulled through the uPVC reinforcement, hinge replacement is required. We carry a wide range of replacement hinges suitable for all common uPVC and composite door systems.

If the keeps on the frame are also worn or have shifted, we adjust or replace these to ensure the locking bolts engage cleanly with minimal resistance.

A Note on Dark-Coloured Doors

Dark-coloured composite and uPVC doors — anthracite grey, black, dark green — absorb significantly more solar radiation than white or light-coloured doors. This means they reach higher surface temperatures on sunny days and expand more. If you have a dark door that is south or west-facing, it is particularly important that the hinges and alignment are set correctly, as the thermal movement will be at the extreme end of normal range.

If your uPVC or composite door is sticking, difficult to lock, or rubbing in warm weather, contact Window Repair Man. We provide door alignment and hinge adjustment services across Leicestershire, Northamptonshire, and Nottinghamshire, usually completing the job in under an hour on a single visit.