Quick answer. The symptom does not on its own establish the correct replacement weatherstrip or a single proven failure. Observe the exact joint and normal closing behavior before replacing a part; if there is a building-water path, alignment problem or safety-rated assembly, obtain model-specific service guidance.
The corner is a junction, not just a strip ending
Seeing light at the bottom, top or side corner of a closed exterior door indicates a visible gap but not necessarily which component is at fault. Possible interfaces to distinguish are the jamb weatherstrip, head strip, door leaf/sweep and threshold/sill intersection. DOE recommends checking light and door fit when looking for leaks, while distinguishing moving-element weatherstripping from stationary-joint sealing. [DOE_AUDIT] [DOE_MOVING]
Make a four-photo corner record
With the door normally closed, record a photo from directly in front of the gap and another from the side showing the contact faces. Open it normally and photograph how the side strip terminates at the sill, how the head piece meets the jamb and whether the bottom sweep is intact. If a corner pad, plug or boot is present, document it without assuming all brands use the same one. Never remove critical hardware or wedge the door open to make a larger gap.
Find the discontinuity without changing the geometry
Compare the corner where light shows to an apparently sound corner on the same door. Note obvious differences in strip seating, damage, weatherstrip length, threshold contact and whether the door leaf sits squarely. Do not double-stack foam or fit a thicker gasket to 'erase' light: that could change normal latching, closing force or accessible clearance. If normal latching is already impaired, record it as a service issue, not a material recommendation.
Dry corner versus wet corner
If the same gap is accompanied by rainwater, separate a weatherstrip-contact problem from sill-jamb flashing/drainage. DOE describes the sill as a distinct water-intrusion vulnerability. Avoid occluding factory drainage or treating water damage as an air-seal-only job. [DOE_FLASH]
A useful parts request
Ask the OEM/service provider to identify every designed component at that corner on an illustrated service view: jamb/head seal, bottom sweep, corner pad, sill cap or end component. Send photos of the receiver and any intact section, and measure a removed sample only if replacement removal is permitted. Ask about model vintage, handing and whether adjustment precedes parts replacement.
Boundary
A photo does not prove the missing part number or certify sealing performance. For rated doors, egress doors and unreliable latch/closer operation, a qualified door specialist must confirm assembly requirements before any material change.
Bounded source notes (checked publisher web pages; 2026-10-12)
- [DOE_MOVING] U.S. Department of Energy, Energy-Efficient Home Improvement Credit Insulation and Air-Sealing Essentials, DOE web resource, retrieved 2026-10-12; locator: Air Sealing: caulk stationary components, weatherstrip moving windows/doors. https://www.energy.gov/cmei/buildings/articles/energy-efficient-home-improvement-credit-insulation-and-air-sealing (Scope: Material selection and rated installations remain product-specific)
- [DOE_AUDIT] U.S. National Park Service, Weatherization of Historic Buildings: Conduct an Energy Audit, NPS web article, retrieved 2026-10-12; locator: Inspect windows and doors for air leaks; draft/airflow assessment section. https://www.nps.gov/articles/000/weatherization-of-historic-buildings-energy-audit.htm (Scope: Building-level diagnostic observations; not an exact part identity or quantitative leakage measurement)
- [DOE_FLASH] U.S. Department of Energy, Building Science Education, Fully Flashed Window and Door Openings: Sill Flashing, BSE web education page, retrieved 2026-10-12; locator: What/Why sections: sill vulnerability, directed drainage, back dam. https://bsesc.energy.gov/energy-basics/fully-flashed-window-and-door-openings-sill-flashing (Scope: Not a diagnosis of a specific leaking doorway; no opening-disassembly instruction)