Most Likely Cause#
A Bosch dryer whose drum will not turn — while the machine still powers on, hums, or heats — almost always has a broken drive belt. The belt wraps the drum and the motor pulley, and when it snaps or slips off, the motor runs but the drum sits still. That is the number-one cause by a wide margin. After it come a failed drive motor, a seized idler pulley or worn drum rollers binding the drum, and a broken belt-tension safety switch that cuts the motor when the belt fails.
The quickest test is to open the door and try turning the drum by hand. A drum that spins freely and loosely with no resistance points at a broken or off belt. A drum that will not turn at all, or turns with heavy drag, points at a seized pulley, worn rollers, or a bound-up motor.
Turn the Drum by Hand#
With the dryer off, reach in and rotate the drum:
- Spins freely and floppily: the drive belt has broken or come off the pulley — the most likely cause.
- Will not budge or drags hard: a seized idler pulley, worn rollers, or a jammed motor is binding the drum.
- Turns normally but the motor hums without spinning it under power: suspect the motor or its start winding.
Do You Have the Right Tools?
Gas leak detector ($130), thermal fuse tester ($95), belt tension gauge, and vent inspection camera ($180). Our technician arrives with $3,000+ in professional tools — your diagnostic is free.
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What Usually Causes It#
The table ranks the causes from most to least common on Bosch dryers.
| Cause | Why the drum won't turn | How common | First fix |
|---|---|---|---|
| Broken or slipped drive belt | The belt no longer links motor to drum | Most common | Inspect the belt; replace if broken or stretched |
| Failed drive motor | The motor cannot turn the drum under load | Common | Test the motor; listen for a hum without motion |
| Seized idler pulley or rollers | A bound pulley or roller stops the drum | Occasional | Inspect and replace the pulley or rollers |
| Broken belt-tension switch | A safety switch cuts the motor when the belt fails | Occasional | Test the belt/tension safety switch |
Drive Belt#
Because a broken belt is far and away the most common cause, it is the first thing to confirm. When the belt snaps, the tension it held is released, which is why the drum suddenly turns freely by hand. On many Bosch models a broken belt also releases a spring-loaded tension switch that shuts the motor off entirely, so a "won't turn" complaint can arrive as a "won't run" one. Opening the cabinet with the power off and inspecting the belt around the drum and motor pulley confirms it quickly; the belt is an inexpensive part.
Motor, Pulley, and Rollers#
If the belt is intact but the drum still will not turn, feel for drag. A seized idler pulley — the spring-loaded wheel that tensions the belt — or worn drum support rollers can bind the drum so the motor cannot move it, sometimes with a groan or a burning-belt smell as the motor strains. If the drum turns freely by hand but the motor only hums under power without spinning, the drive motor or its start winding has likely failed. Each is confirmed with the cabinet open and the power off.
Quick Diagnostic Sequence#
- With the dryer off, turn the drum by hand and judge free versus bound.
- Open the cabinet (power off) and inspect the drive belt.
- Check the idler pulley and drum rollers for seizing and drag.
- Test the belt-tension safety switch if the motor will not run.
- If the belt and pulley are good, test the drive motor.
Safety: unplug the dryer before opening the cabinet, and on gas models shut off the gas supply as well. Do not force a bound drum by hand with force — a seized roller or pulley needs replacing, not muscling.
Safety First — Know the Risks
Gas dryers carry carbon monoxide and explosion risk. Even electric dryers involve 240V circuits that can deliver a fatal shock. Our techs are licensed and insured — let them handle the risk.
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Repair or Replace#
A drive belt, idler pulley, and drum rollers are all inexpensive parts, so a Bosch dryer with a non-turning drum is usually very worth repairing. The one costlier part is the drive motor; on an older dryer a failed motor combined with other worn drive parts is the point to weigh a repair against replacement. If you would rather not open the cabinet, you can book a diagnostic visit to have the belt, pulley, and motor tested.
Appliance Repair Technician · 8 years experience
Experienced technician with 8 years specializing in dishwasher repairs and European appliance brands including Bosch and Thermador.
