Quick answer
Composite door threshold problems - water at the base, a visible worn track, or a draught felt low down - are nearly always a worn gasket or a threshold that's dropped slightly out of level, both cheap and quick to put right. Most modern thresholds are a screw-fixed aluminium extrusion that can be repaired or replaced in under an hour.
Overview
The threshold takes the most abuse of any part of the door - foot traffic, weather, cleaning. Threshold seals and gaskets are cheap and replaceable in under an hour.
Symptoms
- Water under the door.
- Visible worn track.
- Draught at the base.
Common causes
- Threshold gasket worn.
- Threshold blade damaged.
- Threshold not level.
The hardest-working part of the door
The threshold takes more day-to-day abuse than any other part of a composite doorset: foot traffic wears the gasket flat, grit and sand grind against the seal surface, salt spray corrodes fixings faster than an inland equivalent, and pressure washing during cleaning can drive water past a seal that would otherwise cope fine with rain.
It's genuinely normal for a threshold to need attention well before the rest of the door shows any wear, and this is one of the most common single-item repairs we carry out.
Recognising the signs
A visible polished or flattened track along the gasket, where the door slab has been rubbing against it for years, is the clearest sign of wear. A draught felt specifically at floor level, rather than around the whole perimeter, points to the threshold rather than the main seal.
Water appearing right at the base of the door after rain, particularly if it seems to come from directly underneath rather than tracking down a wall, is the third common symptom and usually means either the gasket has failed or the threshold has dropped slightly out of level.
Threshold not level: a less obvious cause
Over years, minor settlement of the doorframe or the surrounding structure can leave the threshold sitting a millimetre or two out of level, which is enough to open a gap at one end even though the gasket itself is in reasonable condition. This is checked with a spirit level laid across the threshold and is worth ruling in or out before ordering a replacement gasket that won't fully solve the problem on its own.
Where the threshold has dropped due to structural settlement rather than wear, packing and re-fixing the threshold extrusion is the correct fix, and it's worth having this checked rather than assuming a new gasket alone will cure it.
Replacing just the threshold
Most modern thresholds are a separate aluminium extrusion, screw-fixed into the frame, with a replaceable rubber or brush gasket insert - which means in the great majority of cases only the threshold itself needs attention, not the whole frame or door. This keeps the job quick and the cost proportionate to what's actually wrong.
On older or unusual installations the threshold may be an integral part of the frame rather than a separate part, in which case replacement is a slightly bigger job - still generally achievable without touching the door slab itself.
Maintenance that extends threshold life
Cleaning the threshold monthly - clearing grit and sand rather than letting it grind into the gasket over time - meaningfully extends its working life, particularly in coastal properties where windblown sand is a constant presence. A quick fingernail test (the gasket should feel springy, not flattened) is a useful way to check condition between full services.
What a threshold service includes
We inspect gasket condition, check the threshold is level and securely fixed, clear drainage where the threshold meets the frame's drainage slots, and confirm the door closes with even compression along the full width of the threshold rather than binding at one end.
Typical repair costs in Cornwall
| Work | Typical price | Notes |
|---|---|---|
| Threshold gasket replacement | £90-£160 | Most common repair |
| Full threshold extrusion replacement | £140-£280 | Where the blade itself is damaged |
| Re-levelling and re-fixing | £95-£180 | Where settlement has occurred |
Guide prices only — we confirm the cost after seeing the door.
When to call a professional
- Threshold replacement.
Prevention
- Clean threshold monthly.
