Troubleshooting: Home Lift Reaches the Ground Floor but the Landing Door Won't Unlock

One of the advantages of designing and programming our own home lifts is that we can usually identify installation issues remotely by understanding how the control logic works.

Recently, one of our customers encountered an interesting problem during installation. Although the lift operated normally between all floors, there was one unexpected behavior on the ground floor.

The Problem

The customer reported the following symptoms:

• The lift could travel normally between all floors.

• When the car arrived at the ground floor and stopped, if pressing the "1" button the ground floor landing door should have been unlocked.

• However, the landing door remained locked.

• At the same time, the hall call display showed that the lift was still moving downward.

At first glance, this seemed like a PLC or door lock problem. Fortunately, the actual cause was much simpler.

Understanding the PLC Logic

Our control program determines the lift's position using floor limit switches.

For the ground floor:

• When the Ground Floor Limit Switch (One Limit) is activated, the PLC recognizes that the lift is positioned at Floor 1.

• If the user then presses the 1 button, the PLC immediately unlocks the ground floor landing door.

Therefore, if the lift is physically at the ground floor but the landing door does not unlock, there is only one logical conclusion:

The PLC is not detecting the Ground Floor Limit Switch.

The next question became:

Why isn't the limit switch being detected?

Checking the Hydraulic Power Unit

We asked the customer to observe the hydraulic power unit while the lift descended.

Our hydraulic system uses three solenoid valves:

• Fast Down Valve (valve two)

• Slow Down Valve (valve one)

• Lock Valve (valve close)

The expected sequence is:

1. As the car reaches the Upper One slowdown limit switch (normally installed about 300 mm above the Ground Floor Limit Switch), the Fast Down Valve(valve two) closes.

2. The lift continues descending at a reduced speed.

3. When the Ground Floor Limit Switch is reached, both the Slow Down Valve(valve one) and the Lock Valve(valve close) close.

4. The lift stops exactly at Floor 1.

The customer confirmed that all three valves operated exactly as expected.

This immediately eliminated electrical faults, PLC programming issues, and valve failures.

Finding the Real Cause

Since the valves operated correctly, we knew the lift had actually triggered the Ground Floor Limit Switch.

So why didn't the PLC recognize Floor 1 afterward?

The answer was that the lift continued moving after triggering the floor limit switch.

Because of its downward momentum, the car travelled beyond the Ground Floor Limit Switch.

Once the switch was released again:

• The PLC no longer knew the car was at Floor 1.

• Pressing button 1 was interpreted as a request to move downward.

• The landing door remained locked because the PLC could not confirm that the car was present at the floor.

Everything the customer observed matched this behavior perfectly.

Two Possible Causes

After reviewing the installation, we identified two possible reasons.

1. The Slow Down Valve Was Adjusted Too Fast

If the slow down valve allows excessive oil flow, the lift still travels too quickly after entering slow speed.

Even though the Fast Down Valve closes correctly, the remaining speed is enough for the car to overshoot the Ground Floor Limit Switch.

2. The Upper One Slowdown Limit Switch Was Installed Too Close to the Floor Limit

The slowdown limit switch should provide enough distance for the lift to decelerate before reaching the floor limit.

If it is installed too close, the lift has insufficient time to slow down.

Although the Fast Down Valve closes at the correct moment, inertia carries the car past the Ground Floor Limit Switch.

The Solution

Relocating the slowdown limit switch would have required additional mechanical adjustment.

To make troubleshooting easier for the customer, we chose the simpler solution first.

We asked the customer to slightly reduce the speed of the Slow Down Valve.

After this adjustment:

• The lift slowed sufficiently before reaching Floor 1.

• The car stopped while still activating the Ground Floor Limit Switch.

• The PLC correctly recognized Floor 1.

• Pressing the 1 button immediately unlocked the landing door.

• The issue was completely resolved.

Lessons Learned

This case highlighted an important installation detail that can prevent similar problems in future projects.

Install the Slowdown Limit Switch Higher

We now recommend installing the Upper One slowdown limit switch at least 300–400 mm above the Ground Floor Limit Switch. And this is suitable for other floors' limit swtiches

This gives the lift enough distance to decelerate before reaching the floor position.

Set the Chain with the Cylinder Fully Retracted

During installation:

• Lower the lift car to the ground floor.

• Fully retract the hydraulic cylinder.

• Tighten and fix the steel chains in this position.

This ensures that when the cylinder is fully closed, the lift car naturally rests at the correct ground floor level and cannot continue descending beyond the floor limit.

Final Thoughts

Many lift problems initially appear to be electrical or PLC faults, but they are often caused by small mechanical adjustments.

In this case, the PLC, sensors, and hydraulic valves were all functioning correctly. The issue was simply that the lift travelled slightly beyond the Ground Floor Limit Switch due to excessive descending speed.

Understanding the sequence of the hydraulic valves and the PLC's floor recognition logic allowed us to diagnose the problem remotely within minutes and solve it with a simple valve adjustment.

We hope this troubleshooting case helps installers facing similar symptoms. If your home lift reaches the floor but the landing door will not unlock, don't immediately suspect the PLC. First check whether the car is still correctly activating the floor limit switch after coming to a complete stop.