Guardian opener chain or belt sags noticeably and slaps the rail during operation.

Safety first: Disconnect power before adjusting chain or belt tension. Do not overtighten; this can damage the opener.

• Locate tension adjustment: On the Guardian rail, find the tension bolt and nut near the trolley or header end.
• Adjust tension: Tighten the nut until the chain/belt has about 1/4–1/2 inch of sag at the midpoint. Do not make it completely tight.
• Inspect for wear: Check the chain for rust and the belt for cracks or missing teeth. Replace if worn.
• Test operation: Restore power and run the door. Listen for reduced slapping or vibration.