Composite Door Won't Close Properly — Diagnosis and Repair
Composite doors are heavier than UPVC (typically 45–55kg vs 30–40kg) which means they put more load on their hinges, expand more in summer heat, and are more sensitive to small misalignments. When one won't close properly, the cause is almost always one of four things — and most are fixable in under an hour without replacing the door.
Cause 1: dropped hinges. The most common cause. Composite door flag hinges wear over thousands of cycles; the door gradually drops 1–3mm on the handle side. Symptom: door catches on the threshold or frame near the bottom corner farthest from the hinges. Diagnosis: open the door fully and look at the gap between the bottom of the door and the threshold across the width — if it's tighter at the handle side, the door has dropped. Fix: most composite door flag hinges have an Allen key adjuster on the side — usually 4mm or 5mm. Raising the door 1–2mm restores alignment.
Cause 2: heat expansion. Composite doors can expand 2–4mm in dimension during a UK summer heatwave. Symptom: door closes fine in winter but sticks or won't shut in July/August. Diagnosis: temporary — leave the door open for 20 minutes in cool shade, then re-test. If it now closes, expansion is your cause. Fix: shift the keeps (the metal plates on the frame that the hooks engage) outward by 1–2mm to give the expanded door clearance. Counter-intuitively, also worth checking the threshold seal — a stiff brush seal can prevent the door closing under marginal alignment.
Cause 3: failed multipoint gearbox. The gearbox is the metal bar inside the door edge that drives the hooks and bolts when you lift the handle. When it fails partially, the handle lifts but the hooks don't fully engage, so the door appears 'closed' but isn't locked. Symptom: handle feels heavier than normal; door pushes open easily once 'locked'; key won't turn smoothly. Diagnosis: try lifting the handle with the door open (so the hooks aren't engaging anything). If the handle is still heavy or won't lift fully, the gearbox itself has failed. Fix: gearbox replacement — Yale Doormaster, GU Secury, ERA Vectis and Fuhr Multisafe are the four common types fitted to UK composite doors.
Cause 4: warped or swollen frame. Less common but does happen — water ingress into the frame (often via failed silicone around the threshold) can cause swelling. Symptom: door has fitted fine for years and suddenly won't close. Diagnosis: look at the frame for any visible distortion, bowing or moisture damage. Run a finger along the threshold and the foot of the frame for any soft or spongy areas. Fix: frame repair is more involved — usually best handled by a composite door specialist rather than a locksmith. We'll diagnose, document and refer where it's the right call.
Five-minute self-diagnosis. Open the door. Look at the gap around the door — top, sides, bottom — across the full width. Equal gaps everywhere means alignment is fine; uneven gaps point to a dropped or warped door. Lift the handle with the door open: if it feels heavy or won't fully lift, it's a gearbox issue. Close the door without turning the key — if it won't latch, it's almost always alignment.
What we charge to fix.
When to stop DIYing and call. Hinge and keep adjustments are within most homeowners' DIY range — Allen keys, a bit of patience. Gearbox replacement involves dismantling the door, sizing the new gearbox correctly to the multipoint mechanism, and re-aligning everything afterwards — usually best left to a working locksmith with the parts in van stock. If you've tried alignment and the door still won't close, calling in is the time-efficient call.