Troubleshooting a Home Lift That Wouldn't Unlock the Ground Floor Door

Installation is the final step before a home lift is put into service, and it is also the stage where small adjustments can have a significant impact on performance.

Recently, one customer contacted us with an issue that seemed unusual at first. The lift could travel normally between all floors, and every function appeared to work correctly except one.

Whenever the lift arrived at the ground floor, pressing the 1 button failed to unlock the landing door. At the same time, the hall display showed that the lift was still descending.

Instead of assuming an electrical fault, we started by thinking about the PLC logic.

Our controller identifies each floor using dedicated limit switches. When the Ground Floor Limit Switch is activated, the PLC records that the lift has reached Floor 1. If the user presses the 1 button while the lift is already there, the controller unlocks the landing door immediately.

Since the door did not unlock, the controller clearly wasn't detecting the Ground Floor Limit Switch anymore.

To narrow down the cause, we asked the customer to watch the hydraulic power unit during descent.

The hydraulic sequence worked exactly as designed. After passing the Upper One slowdown limit switch, the Fast Down Valve closed. The lift continued downward at low speed before reaching the ground floor, where the Slow Down Valve and Lock Valve closed.

Everything appeared normal.

That observation actually made the diagnosis much easier.

If the hydraulic valves were operating correctly, then the lift had definitely reached the floor limit. The only logical explanation was that the car continued moving slightly after passing the limit switch. Once it travelled beyond the switch, the PLC lost its floor reference, making it impossible to unlock the landing door.

Two factors could cause this situation.

One was an overly fast Slow Down Valve adjustment, allowing the lift to maintain too much speed during final approach.

The other was installing the slowdown limit switch too close to the floor limit switch, leaving insufficient distance for proper deceleration.

Rather than relocating the switch, we first adjusted the Slow Down Valve to reduce the descent speed.

The result was immediate. The lift stopped exactly where it should, the Ground Floor Limit Switch remained activated, and the landing door unlocked normally.

This experience also led us to update one of our installation recommendations. We now suggest positioning the slowdown limit switch approximately 300–400 mm above the floor limit switch whenever possible. We also recommend tightening the steel chains while the hydraulic cylinder is fully retracted and the lift car is positioned exactly at the ground floor.

Sometimes the most effective troubleshooting doesn't involve replacing components at all. Instead, it comes from understanding how the PLC, hydraulic system, and mechanical installation all work together.

For installers, paying attention to these small details can save hours of unnecessary troubleshooting and ensure the lift performs exactly as intended from day one.