Automatic Door Fault Finding: Common Swing and Sliding Door Problems

October 5, 2026

Automatic door faults are not always caused by the part that first looks suspicious.

A swing door that won’t open fully might have a perfectly good operator, but the opening-face safety sensor is seeing a cobweb, a dirty lens, a reflection or even part of the door itself.

A sliding door that keeps reopening might not have a controller fault at all. It could be a sensor issue, a tight roller, something in the track or a door leaf that’s dragging slightly.

For an experienced engineer, fault finding is normally about working out what the door is trying to do, what’s stopping it and what input the controller is seeing at the time.

This guide covers some of the more common swing and sliding door faults, with practical checks before parts are ordered or major components are changed.

Safety note: Automatic pedestrian doors contain mains-powered equipment, moving parts and safety-critical devices. Diagnosis, adjustment and repair should only be carried out by suitably competent personnel. Safety devices should never be bypassed just to get a door working. Once repairs are complete, the full door should be tested and left compliant with the relevant safety requirements and risk assessment, including BS EN 16005 where applicable.

Before You Start: Watch the Door

Before taking covers off, watch a few cycles.

That sounds obvious, but it tells you a lot.

Look at what position the door starts from, where it stops, whether the fault happens every time and whether it changes when someone approaches from a different direction.

Also look at what’s around the entrance.

Has someone put a plant near the sensor?

Has a new floor mat appeared?

Has the floor been polished?

Has a sign or display been moved?

Has another contractor worked on the door recently?

A lot of faults are caused by something that has changed around the entrance rather than something failing inside the operator.

It is always worth starting with the actual symptom before jumping to the component you think might have failed.

Automatic Swing Door Fault Finding

1. Automatic Swing Door Will Not Open

If the door is sitting closed and doing nothing, start with the easy checks first.

Is the operator powered?

Is the selector in the correct position?

Is the door actually receiving an activation signal?

A selector left in Off, Manual or Locked can look like a fault when there is nothing wrong with the operator at all.

If the door should be opening, check the activation devices.

That could be:

Push pad.
Touchless switch.
Microwave sensor.
Radio receiver.
Access-control relay.
Interconnecting wiring.

If the activation signal is reaching the controller but the door still won’t move, then start looking at what might be preventing the opening cycle.

An opening-face safety sensor could be active.

A lock may not be releasing.

The door itself may simply be too tight.

With the system made safe, make sure the leaf moves freely.

Check for:

Tight hinges.
Failed pivots.
Door rubbing on the frame.
Door catching the floor.
Damaged arm.
Incorrect arm geometry.
Tight weather seals.
Door closer resistance.
Mechanical lock still engaged.

If the door is hard to move manually, don’t expect the operator to hide the problem forever.

Sort the mechanical issue first.

2. Swing Door Opens, But Will Not Open Fully

If a swing door gets part way open and then stops, the opening-face safety sensor is one of the first things worth checking.

It doesn’t take much to upset a sensor.

A cobweb across the lens, dust, dirt, a reflection from the floor or the sensor picking up part of the door or arm can be enough to stop the opening cycle.

Check for:

Cobwebs.
Dirt or dust on the sensor.
Marks or contamination on the lens.
Water or condensation.
Reflective floors.
Objects near the swing path.
Incorrect field setup.
Sensor detecting the arm.
Sensor detecting the leaf.
Sensor detecting a nearby wall or structure.

One useful clue is whether the door stops at almost exactly the same angle each time.

If it does, watch the safety sensor LEDs while the door is opening.

If one changes state just before the door stops, you’re probably looking in the right place.

Don’t forget that a door-mounted sensor is moving through the opening cycle. It may look fine while the door is closed, then start seeing something once the leaf reaches 40, 60 or 80 degrees.

There are other possibilities too.

The door may have lost its setup.

The opening angle may be wrong.

The mechanical stop may have moved.

The arm may be damaged.

The hinges may tighten up at one point.

The door could also be fighting wind or closer resistance.

Turning the power up normally isn’t the answer.

If the door is tight at one particular point, find out what it’s fighting before changing any force settings.

3. Swing Door Opens But Will Not Close

If the door opens normally and then just sits there, ask one question first:

What is telling it to stay open?

Quite often, the controller is simply seeing a permanent activation signal.

That could come from:

Microwave sensor.
Push pad.
Touchless switch.
Access-control relay.
Radio receiver.
Damaged cable.
Shorted activation input.

Watch the activation input and see if it clears after the person has gone through the doorway.

If it stays active, work backwards from there.

The closing-face safety sensor is another common cause.

It may be seeing a person, but it may also be seeing:

Dirt.
Cobwebs.
A reflection.
The floor.
Part of the door.
A damaged cable.
Something that has been moved into the detection field.

And before spending half an hour fault finding, check the selector isn’t simply set to Hold Open.

It happens.

4. Swing Door Starts Closing Then Reopens

If the door starts closing and then changes its mind, something has told the controller to reopen.

That normally comes down to one of three things:

A new activation.
A safety detection.
Mechanical resistance.

Start with the activation sensor.

Its detection field may be too large or aimed in the wrong direction.

It might be seeing:

People walking past the doorway.
Traffic outside.
Another automatic door.
Moving displays.
Trees or plants through glazing.
Someone moving parallel to the entrance.

Then look at the closing-face safety.

If it only changes state at one particular door angle, contamination or field setup is worth checking.

Mechanical resistance can cause the same sort of behaviour.

Look for:

Door dragging.
Threshold contact.
Tight hinges.
Finger protection rubbing.
Weather seals.
Frame movement.
Arm alignment.

If it reverses at the same point every time, that is usually a useful clue.

5. Swing Door Keeps Opening By Itself

An automatic door opening on its own is often described as ghosting.

There is normally a reason for it.

The first place to look is the activation input.

Watch the sensor or controller indication and see if the input changes when the door opens unexpectedly.

If it does, follow that signal.

Common causes include:

Microwave sensor field too large.
Push pad sticking.
Touchless switch too sensitive.
Moisture in an outdoor switch.
Loose wiring.
Broken conductors.
Damaged door loops.
Access-control relay sticking.
Water ingress.

Intermittent cable faults can be particularly annoying because they may only appear when the door moves.

If the fault comes and goes with the door position, inspect anything that flexes.

6. Swing Door Is Slow, Struggling or Noisy

A slow or noisy swing door doesn’t automatically mean the motor or gearbox has failed.

Start with the mechanical side.

Check:

Hinges.
Pivots.
Arm joints.
Door alignment.
Fixings.
Door closer.
Floor contact.
Weather seals.
Operator mounting.
Output shaft movement.

Listen to where the noise is coming from.

A noise that happens all the way through the cycle is different from one that appears at one specific point.

A loose arm fixing can make a nasty noise.

So can a failing gearbox.

The trick is not assuming the loudest noise must be the most expensive fault.

7. Swing Door Electric Lock Will Not Release

A lock fault is not always a lock fault.

Sometimes it is a timing or alignment issue.

First check whether the lock is getting its release command.

Then check whether it actually releases.

Possible causes include:

No lock power.
Wrong voltage.
Failed power supply.
Wiring fault.
Lock relay fault.
Misalignment.
Door pressure against the lock.
Door leaf dropping.
Incorrect release timing.
Damaged lock.

If the lock releases perfectly when the door is slightly relaxed but struggles when fully closed, look at alignment before replacing the lock.

A door putting constant pressure against the lock can make a healthy lock look faulty.

8. Swing Door Works Intermittently

Intermittent faults usually take longer because the door behaves perfectly as soon as you arrive.

Try to work out what changes when the fault appears.

Does it happen when:

The weather is hot?
The door has run several times?
The leaf reaches one position?
It rains?
The building is busy?
The door vibrates?

Typical causes include:

Loose terminals.
Broken conductors.
Intermittent sensors.
Failing power supplies.
Damaged door loops.
Moisture ingress.
Mechanical resistance.
Locks sticking occasionally.

Intermittent doesn’t necessarily mean complicated.

Quite often it is a loose connection or broken cable that only fails when it moves.

Automatic Sliding Door Fault Finding

Sliding doors have a few more mechanical parts to think about.

Rollers, tracks, guides, belts and carriages all have a part to play, so don’t go straight to the electronics.

If the door doesn’t move smoothly, start there.

9. Automatic Sliding Door Will Not Open

Again, start with the basics.

Is there power?

Is the selector in the correct mode?

Is the controller seeing an activation?

Check:

Microwave sensor.
Push button.
Access control.
Key switch.
Selector.
Wiring.
Safety inputs.
Locking system.

If the operator receives a signal but nothing moves, work out whether the door is locked or mechanically stuck.

Look at:

Door leaves.
Rollers.
Track.
Bottom guides.
Belt.
Belt connection.
Carriages.
Anti-rise.
Mechanical stops.
Foreign objects.

Something as simple as a small stone or damaged guide can stop an otherwise healthy operator.

10. Sliding Door Opens But Will Not Close

If a sliding door opens normally but stays open, the controller is often seeing either a permanent activation or a safety input.

Start with the activation sensor.

Make sure it clears once traffic has passed.

Then look at the threshold safety.

Check for:

Dirt.
Cobwebs.
Water.
Debris.
Objects in the field.
Floor changes.
Incorrect setup.
Sensor movement.
Wiring faults.

This is one of those faults where the door may actually be doing exactly what it is supposed to do.

If the safety system believes somebody is still in the doorway, it should stay open.

The job is finding out why the input is active.

11. Sliding Door Starts Closing Then Reopens

This is one of the more common sliding-door faults.

There are normally two main areas to investigate.

The first is the safety system.

The second is mechanical resistance.

If the safety sensor is active, check setup, contamination and the detection field.

If the safety input is clear, inspect the door movement.

Look for:

Dirty track.
Damaged rollers.
Worn bottom guide.
Door rubbing.
Belt issues.
Carriage wear.
Brush seals.
Threshold contact.
Debris in the door path.

If the door reverses at roughly the same point every time, inspect that area closely.

That repeatable position is often the clue.

12. Sliding Door Does Not Open Fully

If a sliding door stops short, first decide whether it is being told to stop there or whether it physically cannot travel any further.

Possible causes include:

Incorrect opening width.
Lost setup.
Poor learn cycle.
Mechanical obstruction.
Track contamination.
Roller damage.
Belt issue.
Mechanical stop moved.
Door leaf catching.
Safety input.
Incorrect position information.

If work has recently been carried out on the entrance, check what has changed.

A door can be perfectly happy with its stored setup until someone moves a stop, adjusts a leaf or alters the mechanics.

13. Sliding Door Is Slow

If a sliding door has gradually become slower, mechanical drag is worth checking first.

Look at:

Rollers.
Track.
Bottom guides.
Belt tension.
Belt condition.
Door alignment.
Brush seals.
Weather seals.
Leaf clearance.

A roller can still turn and still be bad.

If it is beginning to fail, it may put a lot more load on the drive system without looking completely seized.

Also check whether anything has been added to the door.

Signs, graphics, replacement glass or extra hardware can all change the load.

14. Sliding Door Is Juddering, Vibrating or Noisy

Noise is useful.

Try to work out whether it follows the door position or the rotation of a component.

A rhythmic noise can point towards a pulley, belt or roller.

A noise in one position can point towards the track or alignment.

A knock when starting or stopping could indicate play in the drive.

Check:

Rollers.
Carriages.
Belt.
Belt teeth.
Drive pulley.
Idler pulley.
Motor mounting.
Door hangers.
Anti-rise.
Bottom guides.
Track damage.
Loose fixings.

Also check the obvious stuff.

Door leaves touching each other or catching a side screen can sound much worse than they really are.

15. Sliding Door Lock Will Not Release

First decide whether you have an electrical lock fault or a mechanical one.

Check:

Release command.
Lock supply.
Wiring.
Lock alignment.
Door leaf position.
Lock engagement.
Leaf adjustment.

If the operator is trying to drive before the lock has fully released, look at sequencing as well.

Repeatedly driving against a locked leaf is only going to create more problems.

16. Sliding Door Keeps Opening With Nobody There

As with swing doors, there is normally an input behind it.

Watch the activation indicator.

Common causes include:

Detection field too large.
People moving parallel to the entrance.
Road traffic.
Reflections.
Moving objects.
Another automatic door nearby.
Loose wiring.
Water ingress.
Intermittent access-control output.
Faulty switch.

If there are two sets of sliding doors in a lobby, make sure one isn’t seeing movement from the other.

That is an easy one to miss.

17. Sliding Door Works Normally Until Busy Periods

If a sliding door only starts misbehaving when the building gets busy, don’t just assume the electronics are overheating.

It may simply be that the problem only appears under repeated cycling.

Check:

Mechanical resistance.
Roller condition.
Motor performance.
Power supply.
Loose connections.
Lock operation.
Belt condition.
Heat build-up.

Also watch how the sensors behave when lots of people are using the entrance.

A marginal sensor setup can look fine when one person walks through but become unreliable once several people are moving through overlapping detection zones.

Sometimes the best way to find the fault is to watch the door when the customer actually sees the problem.

18. The Door Worked Until Somebody Cleaned It

This sounds like a joke until you’ve seen it a few times.

Cleaning can easily change:

Sensor position.
Sensor lenses.
Door alignment.
Selector switch position.
Cable position.
Floor reflectivity.
Detection conditions.

Water can also find its way into places it shouldn’t.

The same applies to decorating, shop refits and flooring work.

If someone says, “It was working yesterday”, it is worth asking what else happened yesterday.

That question can save a lot of time.

Check Inputs Before Replacing Outputs

One of the best habits in automatic door fault finding is checking what the controller is being told before changing the part that isn’t moving.

If the door won’t open, is a safety input active?

If it stays open, is activation being held on?

If it reverses, has a safety or obstruction input changed?

If the motor appears weak, is the door mechanically tight?

If the lock looks faulty, is the leaf loading against it?

The operator is only reacting to the information it receives.

A sensible fault-finding sequence is usually:

Activation → Safety → Control → Locking → Drive → Door Movement

That order will often save you replacing the wrong thing.

What Should a Parts Buyer Ask Before Ordering?

Parts buyers can save a lot of unnecessary returns by asking a few questions before placing the order.

Useful questions include:

What is the actual symptom?
Does the operator have power?
Is the activation input working?
Are any safety inputs active?
Does the door move freely?
Is the lock releasing?
Does the fault happen in the same position every time?
Has the sensor been cleaned and checked?
Has the setup or learn cycle been completed?
Has any recent work been carried out?
Has the suspected part actually been tested?

Sometimes the answer to one of those questions changes the order completely.

Repair the Part or Retrofit the Operator?

Not every fault means replacing the operator.

If the door is generally sound and the fault is a sensor, switch, lock, roller, belt, battery or similar service item, repairing the existing system is often the sensible choice.

There does come a point, though, where continuing to repair an old operator stops making sense.

A retrofit may be worth considering when:

Major parts are obsolete.
Replacement boards are unavailable.
Motors or gearboxes are no longer supported.
Multiple components are failing.
The operator has become unreliable.
Previous modifications have made the system difficult to maintain.
Repair costs are starting to outweigh the value of the equipment.
The customer wants better long-term reliability.

On sliding doors in particular, it may be possible to keep suitable leaves and screens while replacing the operator, control system and associated safety equipment.

Sometimes that is a much better long-term fix than continuing to chase obsolete parts.

Don't Forget the Simple Faults

Experienced engineers often expect the difficult fault.

Sometimes that makes the simple one easier to miss.

Before replacing an expensive component, check:

Cobwebs.
Dirty sensors.
Loose wires.
Stones in the track.
Doors rubbing.
Selector in the wrong mode.
Stuck push pads.
Locks not releasing.
Sensors looking at something they shouldn’t.
Door setup not matching the mechanics.

Good fault finding is not about replacing the most parts.

It is about finding the real cause, fixing it properly and leaving the door working reliably.

And quite often, the quickest route to the answer is watching the door before opening the operator.

Back to blog