The four sensors on a typical UK home lift door
- Reed switch (interlock proof). A magnetic sensor that tells the controller the door is closed and latched. Silent in operation, fails hard when the magnet drifts or the switch cracks.
- Light curtain (infrared beam). A row of paired emitters and receivers up each side of the doorway. Any object breaking the beam reverses a closing door.
- Safety edge (pressure strip). A rubber strip on the leading edge of the door that reverses closure on any physical contact.
- Mechanical latch (final proof). A hooked bolt that must physically drop into the frame slot before the safety chain closes.
All four must be happy for the door to be treated as closed. A fault in any one takes the whole lift out of service.
Reed switch failures
Reed switches fail in two ways: the magnet drifts out of alignment (usually a knocked door or slammed frame) or the switch itself cracks from repeated impact. Symptom is identical either way: the door closes visually and mechanically, but the controller reports it as open.
This is engineer work — the switch is buried in the frame or door edge and its position is set with a feeler gauge. Do not attempt to re-glue or re-align it yourself; a switch in the wrong place will ‘work’ but the door will not be safe.
Light-curtain cleaning: the one thing you can do yourself
Safe to check yourself
Light-curtain sensors are the small round or rectangular lenses at 4–8 evenly-spaced points up each door jamb. Dust and pet hair build up on them and eventually break the beam even when the doorway is clear.
- Isolate the lift at the wall switch — you do not want the door closing on your hand.
- Wipe each lens with a dry microfibre cloth. Both sides of the doorway.
- Do not use any solvent, damp cloth, glass cleaner or paper towel — all will damage the lens coating over time.
- Re-energise, cycle the door, done.
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Describe your symptom →Safety-edge failures
The pressure strip on the leading edge of the door can be crushed by a dropped shopping bag, chewed by a puppy, or split by decades of thermal cycling. Symptom: the door starts to close, immediately reverses, and the controller logs a safety-edge trip. You can see damage — a visibly torn or squashed strip is your diagnosis. Replacement is a service-visit part and takes about 30 minutes.
The mechanical latch — the one that clunks
The last centimetre of door travel is the mechanical latch dropping into a slot in the frame. You can hear it as a soft ‘clunk’. If that sound has disappeared and the door now closes with a soft ‘whump’ instead, the latch is not seating — either the door has dropped on its hinges, or the strike plate on the frame has been knocked out of line. This is not user-serviceable; do not try to bend the strike plate back with pliers.
When several sensors fail at once
Stop — call an engineer
If more than one door sensor reports a fault in the same day — say a light-curtain trip in the morning and a reed-switch fault by evening — do not keep resetting. This is a common early sign of controller board failure, wiring loom damage or (rarely) a water ingress event you haven't yet noticed. Isolate the lift and call an engineer with the fault sequence written down.
Frequently asked questions
- Can I disable a nuisance safety-edge trip while I wait for the engineer?
- No. Disabling any door safety sensor on a UK home lift is illegal under the Machinery Directive and — for workplace lifts — a LOLER offence. If the trip is genuinely nuisance, isolate the lift and wait.
- How often should door sensors be cleaned?
- Light curtain lenses benefit from a wipe every 3–4 months in a normal household, more often with pets or in dusty environments. Reed switches, safety edges and mechanical latches need no owner cleaning — they are inspected on the annual service.
- The door closes fully but the lift still shows ‘door open’. What now?
- Reed switch or latch fault. Both are engineer-only. Isolate the lift, log the code and phone the service provider — do not try to lubricate or adjust the latch yourself.
- Are older mechanical doors more reliable than modern power doors?
- In simple terms, yes — fewer sensors means fewer failure modes. But mechanical doors need physical effort to operate, which can be an accessibility barrier. Both types are LOLER-compliant when fitted and maintained correctly.
- Does the door sensor draw power even when the lift is idle?
- Yes — the interlock proving circuit is live whenever the lift has mains. This is why isolating the lift at the wall is the first step in any door-sensor work; the second is confirming with a proving unit that the circuit is actually dead.