Repair or replace?
If the unit is relatively new, a repair is usually better value. If it is old, parts are hard to find, or the motor has failed and costs close to a new unit, replacement is worth pricing.
Warning signs
Burning smell, breaker trips, loud grinding, repeated shut-offs, or weak suction after the bag, filter and pipe are checked.
Keep the pipe
Pipe usually lasts the life of the house, so most replacements only change the power unit. See replacement and upgrades.