Door faults dominate callback statistics on almost every maintenance route. They are also the most repairable, because every failure mode is visible and measurable – it is rarely a mystery, just work that was finished too early.
Operator types and what each is good at
| Type | Strengths | Characteristic faults |
|---|---|---|
| Centre-opening, linear cam | Simple, mechanical, tolerant of dirt | Cam follower wear, roller flat spots, stretched chain |
| Centre-opening, VVVF belt | Smooth, quiet, tunable | Encoder loss, belt tension, learn/teach data lost after power events |
| Two-speed side opening | Long life on older cars | Fast/slow cam timing, arm wear, clutch slippage |
| Manual (swing or sliding) | No operator to fail | Closer adjustment, latch and interlock wear, gate contactors |
The four things that actually matter
1. Alignment across the sill
Measure car door to hoistway door alignment at top, middle and bottom of the panel travel with the doors closed and again part-open. The doors must not rub the sill, and the gibs must not bottom out. Alignment is a measurement, not an opinion.
2. Gibs and rollers
Worn gibs let the panel sit at a different angle closed than open, so the interlock engages differently on each floor. Replace gibs before adjusting interlocks – otherwise you adjust to a moving target.
3. Interlock and closed-circuit contacts
Check the mechanical engagement first, then electrical continuity with the door just closed, and again with the panel pressed lightly by hand. A contact that drops out under slight pressure will produce intermittent between-floor stops that never reproduce on the landing.
4. Reopening device
Confirm the detector covers the full width of the entrance and reacts within the required distance and time. On light curtains, inspect the edge for impact damage and clean the lenses; on mechanical edges, check the travel and the switch, not just the sound it makes.
An alignment procedure that lasts
- Park the car, apply the stop switch, and confirm the pit and top-of-car are safe to work in.
- Level the car precisely. Door work done on an unlevelled car will not stay right.
- Check the sill and the gib clearances cold, then run the doors and re-check hot.
- Set the panels parallel to each other, then set the interlock engagement, then verify with the door slightly loaded.
- Re-teach/learn the operator only after the mechanical geometry is correct, and record the teach date.
- Run a full cycle on every landing, observing the door at each one – problems usually appear at one landing, not all.
See also the safety chain for how door circuits sit inside the chain, and browse forum threads on door operator faults for model-specific experience.