Short answer. On the Therma-Tru system addressed by the 2017 troubleshooting guide, a missing corner seal pad is a different diagnosis from missing, painted, cracked or torn jamb weatherstrip. source Do not order a full vertical strip simply because daylight appears near the lower corner. First determine whether the small local pad is present and whether the longer jamb strip is continuous.
Where this distinction applies
The manufacturer's 2017 air/light-leak table is the reference for this comparison, not a promise that the same part fits every Therma-Tru entry. The Project Center's corner-pad installation step expressly applies to inswing doors. source If the swing, sill design, or original door-system documentation is unknown, treat the part as unidentified rather than guessing from its appearance.
Read the corner before buying
| What you can observe | Which possibility to document | Why the distinction matters |
|---|---|---|
| An empty-looking spot right where a jamb meets the sill, with the upright strip still apparently present | Local corner pad candidate | Missing lower pads have their own entry in the 2017 air/light diagnosis. source |
| An interrupted, torn, hardened-looking, paint-covered, or missing length along the jamb | Jamb weatherstrip candidate | Therma-Tru lists strip defects separately. source |
| Both appear intact but light remains | Unresolved; inspect closure contact and obtain the exact system guide | The two visible parts cannot establish an exclusive cause. |
Four checks without dismantling the threshold
- Confirm swing. Stand inside, note which way the slab moves, and record an identifying label or paperwork. Use the Step 9 pad description only if the referenced inswing configuration is established. source
- Photograph the whole corner. Include the threshold, vertical jamb strip and adjoining door edge in one shot, then take a closer unobstructed view.
- Trace the strip visually. Compare intact sections at mid-jamb and near the sill; photograph any separation or coating rather than pulling the strip free.
- Match evidence, not color. Compare the observations with the 2017 p.4.3 categories. Neither a pad that looks similar nor a strip that presses into a groove proves compatibility with a later assembly.
Decision and stop points
Pad-location evidence only: record “possible missing lower corner pad,” verify inswing and the exact sill/jamb assembly before purchase. Long-strip damage: record the affected side and original attachment style; use the correct jamb-weatherstrip procedure rather than a threshold-parts diagram. Uncertain or mixed clues: keep both candidates open and obtain the appropriate edition of the manufacturer instructions. No leak or energy-performance result is guaranteed by replacing either item.
Primary sources and claim locator register
- — Therma-Tru original, 2017 Site Manual — SITE 4, US; p.4.3, lower corner pad row. Publisher document.
- — Therma-Tru original, 2017 Site Manual — SITE 4, US; p.4.3, first three weatherstrip rows. Publisher document.
- — Therma-Tru original, US HTML undated, accessed 2026-10-11; Step 9, opening statement (in-swing only). Publisher document.
Evidence and safety boundary
Therma-Tru’s 2017 SITE 4 manual (printed p. 4.3) discusses lower corner-pad and jamb-weatherstrip locations as different observations. First note where the visible gap or damaged component sits: at the lower corner near the sill, or along the jamb. Record door handing, sill style and a clear photograph before requesting the matching replacement instructions. A photograph alone does not confirm the cause of a leak or establish interchangeable parts.