the night light won't turn off even when i press the button or have it set to off in the app.

Diagnosis

The persistence of the night light on the Levoit Core 400S typically stems from a synchronization failure between the VeSync app's cloud command and the local firmware on the purifier's control board. When you press the physical button or toggle the app switch and the light remains on, the device has entered a "soft-lock" state where the logic board is receiving the command but failing to trigger the relay that cuts power to the LED array. This is often caused by a corrupted cache in the onboard memory or a conflict following a firmware update that didn't fully initialize. In some cases, it is a capacitive touch failure where the physical button on the top panel is no longer registering a complete circuit, but since the app also fails to kill the light, the issue is almost certainly rooted in the firmware's execution layer rather than a hardware failure of the LED itself.

How to Fix It

To resolve this, you must perform a hard power cycle to clear the volatile memory (RAM) on the control board and force a re-sync with the VeSync servers.

1. Power down the unit using the physical power button on the top touch panel.
2. Physically disconnect the power cord from the wall outlet. Do not simply turn off a power strip; the unit must be completely severed from the AC source.
3. Wait exactly 3 minutes. This duration is critical to ensure the capacitors on the internal circuit board fully discharge, which wipes the temporary error state.
4. While the unit is unplugged, press and hold the Power button for 10 seconds to drain any remaining residual electricity.
5. Plug the unit back into the wall outlet.
6. Power the device on. Before opening the app, press the physical Light button on the touch panel. Cycle through the brightness levels (High, Low, Off) manually.
7. Once the light is off via the physical button, open the VeSync app and verify that the light status now reflects "Off."

If That Didn't Work

If the hard reset fails, try these advanced troubleshooting steps:

• Perform a Factory Reset: Press and hold the Power button and the Fan Speed button simultaneously for about 5-10 seconds until the display flashes or the unit beeps. This wipes all custom settings and network configurations, forcing the firmware to revert to its base state. You will need to re-pair the device to your Wi-Fi after this.
• Force a Firmware Update: Open the VeSync app, go to Device Settings, and check for a firmware update. If one is available, install it immediately. If you are already on the latest version, toggle the "Sleep Mode" on and off several times; Sleep Mode is programmed to override the night light, and triggering this specific logic path can sometimes "kick" the light relay into the off position.
• Clear App Cache: On Android, go to Settings > Apps > VeSync > Storage and Clear Cache. On iOS, delete the VeSync app entirely and reinstall it. A corrupted local app cache can send conflicting "On/Off" packets to the device, causing the purifier to ignore the command.
• Inspect for Panel Contamination: Use a microfiber cloth dampened with 70% isopropyl alcohol to clean the top touch panel. A thin layer of oily residue or dust can create a "phantom touch" or prevent the capacitive sensor from registering your finger, making the button seem unresponsive.

Heads Up

• Avoid using abrasive cleaners or bleach on the touch panel, as this can strip the capacitive coating and permanently disable the light and power buttons.
• If the light flickers before staying on, this indicates a failing capacitor on the control board, which requires a professional repair or warranty claim.
• Always ensure your 2.4GHz Wi-Fi signal is stable; frequent disconnects during firmware updates are the primary cause of these "ghost" settings and unresponsive controls.
• Keep the air intake vents clear of dust; overheating of the internal logic board can occasionally lead to erratic behavior in the LED control system.