Quick answer
A poorly installed composite door usually shows as an uneven reveal, a frame that flexes when pushed, poor seal compression or keeps fixed only into the plastic frame rather than masonry. Most poor installs can be remediated with re-fixing, re-shimming and re-sealing rather than a full replacement, provided the frame itself isn't structurally compromised.
Overview
Bad installations are common. The signs are consistent: uneven gaps, poor seal compression, frame moving, keeps only into the plastic frame. Most can be remediated without a new door.
Symptoms
- Uneven gap around the door.
- Draughts or leaks.
- Frame moves when door slams.
- Keeps not screwed into masonry.
Common causes
- Rushed installation.
- Wrong fixings.
- Frame not shimmed correctly.
Why bad installs are so common in Cornwall
Composite doors look simple to fit, and that's exactly why so many go in badly. The door slab itself is forgiving, but the frame underneath has to be set level, plumb and square into an opening that, especially in older Cornish cottages, is rarely any of those things. Granite reveals, cob walls and settled stone openings all move the goalposts on a standard install, and a rushed team working to a tight day rate will often pack the frame just enough to get it to close, not enough to make it right.
We see a steady stream of call-outs from up-country installers who fitted a door on a single visit, took payment, and were gone before problems surfaced. Coastal exposure accelerates the fallout — a gap that would be a minor nuisance inland becomes a proper leak once south-westerly rain gets behind it. Holiday-let owners are particularly exposed because nobody notices a slow water ingress problem until a guest complains or a floor starts to lift.
The tell-tale signs to check for
You don't need to be a fitter to spot most poor-install symptoms. Stand outside and look along the top of the frame against the brick or render — if the gap narrows or widens noticeably from one side to the other, the frame was never set square. Push firmly on the frame near each hinge and keep with the door open; there should be zero movement. Any flex means fixings are missing, too short, or not backed with packers.
Inside, check that the door closes with light, even pressure on the handle — if you have to lean into it, the frame is likely racked. Run a hand around the perimeter seal with the door shut; it should compress evenly all the way round, not just at the top.
- Uneven reveal, especially top to bottom
- Frame moves or flexes under hand pressure
- Door needs extra force to close or lock
- Draught from the frame perimeter, not the door edge
- Keep screws visible but clearly not reaching brick
What a correct installation actually involves
A proper composite door fit starts with removing the old frame back to a clean opening, checking the opening for level, plumb and square, and packing the new frame with shims at every fixing point before a single screw goes in. Fixings should run through the frame, through packers, and into sound masonry — not just into render or a timber sub-frame that's seen better days. On exposed coastal walls we'll often use additional fixing points and longer screws than a standard inland install would need.
Once the frame is fixed, the gap between frame and structural opening gets filled with low-expansion foam, not left hollow, and the external joint is finished with a proper bead of low-modulus silicone — not a smear. Only then does the door slab get hung, hinges adjusted, and the multi-point lock checked for smooth engagement at every point.
What we do when we're called to fix someone else's work
Our first visit is always a proper audit rather than a quote off a couple of photos. We check diagonals, push-test the frame at every fixing, inspect keep screws where visible, and look at the external sealant line. That tells us whether this is a re-fix — extra fixings, packers and re-sealing — or whether the frame has to come out and go back in properly.
Most jobs land in the first category. Re-fixing a frame that's simply under-screwed typically takes two to three hours and doesn't require removing the door slab. Where the frame is genuinely racked or was set with the wrong reveal, a full removal and refit is the only honest answer, and we'll say so rather than papering over it.
Building Regulations and CERTASS compliance
Replacement external doors are controlled work under Building Regulations Part L (thermal performance) and Part Q (security) in England, and equivalent standards apply across the rest of the UK. A CERTASS-registered installer self-certifies the work and notifies building control on your behalf, and you should receive a compliance certificate for your records — essential if you ever sell the property.
If your original installer never issued one, that's a red flag worth chasing, particularly for anyone marketing a holiday let where guests' safety and the property's legal compliance both matter. We can advise on getting retrospective compliance sorted where an installer has gone quiet or out of business.
When remediation isn't enough
Occasionally the frame itself is the wrong size for the opening, or has been cut and packed so aggressively that there's no sound fixing point left. In those cases, remediation would be treating the symptom rather than the cause, and we'll recommend a proper refit using a correctly sized frame. This isn't the outcome we lead with — it's more expensive and more disruptive — but pretending a badly undersized frame can be shimmed into permanence just delays the same conversation by a year or two.
What it actually costs to put a bad install right
Numbers help more than vague reassurance when you're deciding whether to chase an installer or just get it sorted. A straightforward re-fix — extra fixings, new packers, re-run silicone — typically runs £120 to £220 and takes an afternoon. A frame that has to come out and go back in properly is a different order of job: £450 to £850 depending on opening type, plus a day or two without a secure front door while you wait for a slot.
The false economy is doing nothing. A frame under-fixed into render rather than masonry will keep moving under wind load, and every winter of movement widens the gap the silicone has to bridge until it fails completely. What's a £150 re-fix this year becomes water damage to a timber sub-frame or internal reveal within two or three seasons, and that repair bill has no ceiling once rot's involved.
Your rights if the installer won't come back
If you paid a UK-based installer and the door isn't fit for purpose, you have rights under the Consumer Rights Act 2015 regardless of what their own terms say — work has to be carried out with reasonable care and skill, and a racked frame or under-fixed frame plainly wasn't. Put your concerns in writing (email, not just a phone call) with photos and dates, and give them a reasonable chance to inspect and correct it themselves before you look elsewhere.
If they've stopped responding or the business has closed, you can still pursue a claim through the small claims track for the cost of remedial work, though realistically most people find it quicker to get the door made safe and compliant first and pursue costs separately. Keep every invoice from any remedial work — you'll need it as evidence of loss if you do take it further.
What good practice looks like when we're on site
A proper remedial visit isn't a five-minute look and a quote by text. We check the opening for level, plumb and square independently of what the existing frame is doing, push-test at every hinge and keep point, and inspect what the current fixings actually caught — brick, block, timber sub-frame, or nothing solid at all. Only once we know exactly what's wrong do we scope the fix, because 're-seal it' and 'refit the frame' are very different jobs with very different price tags.
We'll also check drainage slots, the head detail, and whether the door was ever certified to Part L and Part Q in the first place, because a poor install and a missing compliance certificate often go hand in hand.
Second homes: why bad installs go unnoticed longest here
Cornwall has one of the highest proportions of second homes and holiday lets in the country, and a poorly fitted door on a property that's occupied for six weeks a year can sit deteriorating for months before anyone notices. Owners relying on a cleaner or agent to flag problems are trusting someone who isn't necessarily looking for a 2mm gap at the head of the frame.
If you own a Cornwall property you don't live in full-time, it's worth having any door installed in the last two years independently checked at the next changeover, particularly before winter lets or a run of empty weeks. A £45–£75 inspection is cheap insurance against discovering a water-damaged reveal on your next visit.
A simple decision framework
If the frame passes a push test with zero movement and the only issue is patchy sealant or a gap under 3mm at one point, re-sealing alone is usually enough. If there's any detectable flex, or the keep screws visibly miss masonry, budget for a re-fix rather than a cosmetic fix — sealant over a moving frame just fails again within a season. If the opening itself was wrong for the frame size supplied, or the frame has been packed more than about 15mm to force a fit, a full refit is the only fix that will still be sound in five years' time.
Typical repair costs in Cornwall
| Work | Typical price | Notes |
|---|---|---|
| Installation audit and diagnosis | £45–£75 | Often credited against remedial work |
| Re-fixing frame with extra fixings/packers | £120–£220 | Most common remediation |
| Re-sealing perimeter (internal and external) | £90–£160 | Where silicone has failed |
| Full frame removal and refit | £450–£850 | Where frame is racked or undersized |
| New door fitted from | £1,395 | Where remediation isn't viable |
Guide prices only — we confirm the cost after seeing the door.
When to call a professional
- For an installation assessment.
Prevention
- Use CERTASS installers.
