How do I check a fire door is still doing its job?

A five-minute inspection covering gaps, seals, hinges, closers and the certification label, and what each failure actually means.

Difficulty: beginner
Time: 20 min
Read: 4 min
Safety: warning

Short answer

Check the gap all round is about 3mm, that the intumescent strip is continuous and undamaged, that there are three CE-marked hinges with every screw present, and that the door closes fully from any angle and latches on its own.

A fire door buys time for people to get out. Almost every failure found in practice is one of a small handful of things — a missing screw, a painted-over seal, a wedged-open door — and all of them are findable in a few minutes.

Safety

A fire door only works as a complete assembly — leaf, frame, seals, hinges, closer and glazing all together. If any element is missing, damaged or non-compliant, treat the door as not fire resisting. In a flat, a house in multiple occupation or a rented property, fire doors are usually a legal requirement and any doubt should go to the landlord, managing agent or your local fire and rescue service, not to a DIY repair.

What you'll need

A £1 coin or a 3mm gauge
A torch
A screwdriver

Step by step

Find the certification.Look on the top edge or the hinge edge for a label, plug or colour-coded pin identifying the door and its rating, usually FD30 or FD60. No label does not always mean no rating, but it means you cannot prove one.
Check the gaps.About 3mm around the top and sides — roughly the thickness of a £1 coin. Larger and hot smoke passes; much smaller and the door may bind when it needs to close.
Check the threshold gap.Typically under 10mm at the bottom for a fire door, and much less where a cold smoke seal is required. A large undercut is a common failure.
Inspect the intumescent strip.It should run continuously in its groove around the top and both sides, be well fixed and not painted over. Painted, missing or damaged strip means the seal cannot expand and close the gap.
Check the smoke brush if fitted.Doors marked FD30S have a brush or fin seal for cold smoke as well. It must be intact and touching the frame.
Count the hinges and the screws.Three hinges, CE-marked, with every screw present and tight. A single missing screw is one of the most frequently found faults and is a genuine failure.
Test the closer.Open the door to 5 degrees, 45 degrees and fully, and let it go each time. It must close fully and latch by itself from every position, including against a normal draught.
Check the door is not wedged or held.No wedges, no hooks, no bin, no over-door hangers. If a door genuinely needs to be held open, that requires a certified hold-open device linked to the alarm.
Look at the leaf itself.No holes drilled through it, no cat flap, no letterplate that is not fire rated, no panel replaced with ordinary glass. Any breach through the leaf ends its rating.
Check the frame is fixed and packed.The frame must be properly fixed to the structure, with the gap behind it filled with fire-rated material rather than ordinary foam.

Tips

A £1 coin is very close to 3mm and lives in your pocket. It is the standard field check.
Do the closer test with the internal doors and windows in their normal positions. A door that latches in still air but not with the landing window open is failing in real conditions.
Check fire doors twice a year alongside the smoke alarms. It takes the same five minutes and the two go together.

Common mistakes

Painting over the intumescent strip — Repeated coats of paint restrain the strip and can stop it expanding at the temperature it is designed for. The door then leaves a 3mm gap to hot smoke exactly when it needs to close it.
Fitting ordinary ironmongery to a fire door — Hinges, latches, closers, letterplates and glazing all form part of the tested assembly. Substituting an untested part means the door as a whole no longer has a rating, whatever the leaf is.

If it doesn't work

Door does not latch from a small opening angle

Cause: Closer too weak or misadjusted, or the latch is stiff — Fix: Increase the closer's latching action and free the latch; if it still fails, the closer is the wrong size.

Gap larger than 4mm at the latch side

Cause: Door dropped or frame moved — Fix: Correct the hinges, or fit an intumescent gap seal designed for over-size gaps rather than packing the frame.

Intumescent strip loose or missing in places

Cause: Damage or removal during decoration — Fix: Replace the whole run with the correct size strip for the door's rating.

Door held open with a wedge

Cause: It is inconvenient in normal use — Fix: Fit a certified alarm-linked hold-open device, or remove the wedge; there is no acceptable middle ground.

Questions people ask

How do I know if a door is a fire door at all?

Look for a label or plug on the top or hinge edge, check for an intumescent strip in the frame or door edge, and note the weight — an FD30 door is noticeably heavy. Without evidence, assume it is not rated.

Can I fit a cat flap in a fire door?

No. Any breach through the leaf destroys the rating, and there is no domestic retrofit that restores it. The door would have to be replaced with a non-fire door, which is not permissible where a fire door is required.

Do I legally need fire doors in my house?

In a standard single-family house, usually only where Building Regulations required them — commonly between an integral garage and the house, and on habitable rooms opening onto the stair in a three-storey house. Flats and HMOs have far broader requirements.