The answer to 'vacuum dirty' is that a dirty vacuum can significantly reduce its suction power and cleaning effectiveness. Common causes include clogged filters, full dust bags, and tangled debris in the hose or brush. Symptoms may include poor suction, scattered debris, and the vacuum overheating or shutting off.
The first step is to check the vacuum's filters and dust bag, and clean or replace them as needed. You should also inspect the hose and brush roll for any clogs or tangles, and clear them out. If the vacuum still isn't working properly after basic maintenance, it may be time to call in a professional cleaning technician to diagnose and repair any deeper issues.