Robot lawnmower fails to detect obstacles and collides hard with trees or walls, even though it has a bumper.

Safety first: Turn OFF the mower and remove the battery before working on the bumper.

• Test bumper movement: Push the bumper in and release. It should move freely and return fully. If not, remove debris from the gap.
• Inspect springs and guides: Open the front housing and check that all springs are intact and correctly seated.
• Verify switch actuation: Ensure that when the bumper is pressed, it physically actuates the microswitch levers. Adjust or replace parts if necessary.
• Replace bumper assembly: If the bumper is cracked or cannot move smoothly, install a new NAC bumper assembly.

Warning: Do not operate the mower if it cannot reliably detect obstacles; this is a major safety risk.