Scrubber Brushes Not Turning: How to Find the Cause Fast

Key takeaways

• Most brushes-not-turning calls are a deck that is not fully lowered, a tripped brush breaker, or a brush motor overload fault.
• Debris wound around the brush or a pad driver jammed on the deck trips overcurrent protection repeatedly.
• Worn brush motor carbon brushes are the most common motor failure and are cheap to replace.
• If only one of two brushes stops, swap tests and a current check isolate the motor quickly.
• Disconnect batteries before reaching under the deck.

When scrubber brushes are not turning, check in this order: the scrub deck is not fully lowered or the brush function is not selected, the brush motor breaker or fuse has tripped, the controller has shut the brush down on an overcurrent fault, debris has jammed the brush, or the brush motor's carbon brushes are worn out. Belt-driven cylindrical decks add a broken or slipped drive belt to that list.

Brush motors draw more current than anything else on the machine, often 20 to 50 amps per motor on walk-behinds and more on large riders, so they are the circuit most likely to trip and the motor most likely to wear. Most fixes in this guide take under 20 minutes.

Check this first

• Is the deck actually down? Most machines only spin the brush when the deck is lowered and a limit switch or actuator position confirms it. A deck that stops a half inch high will not start the brush.
• Is the brush function on? Many panels have a separate scrub on/off button, or a one-touch scrub mode that must be selected. Some brushes only turn when the bail or throttle is engaged and the machine is moving.
• Breakers and display. Look for a popped brush breaker and any message about brush overload, brush current or brush motor.
• Look under the deck. String, shrink wrap, banding strap, zip ties and wire wrap around brush hubs and stall them.
• Is a brush or pad driver installed and seated? A pad driver that has fallen off and wedged against the shroud stops everything.

How the brush circuit works

On a typical disc machine, the controller (or a brush relay or contactor on simpler machines) switches battery power to one or two permanent magnet DC brush motors once the deck is down and scrub is selected. The controller monitors brush current; when current rises above a set limit for a set time, it shuts the brush off and posts a fault. That protection saves the motor, but it means any extra load (too much down pressure, an aggressive pad on a grippy floor, a jam) can stop the brush with no motor fault at all.

Cylindrical decks usually drive two counter-rotating rollers from one or two motors through belts. Orbital decks use an eccentric drive. The logic is the same; the drive path is different. See scrub deck types.

Diagnostic sequence

Key off and disconnect the battery connector before you touch the deck, belts or motor wiring.

1. Confirm deck lowering. Watch the deck as you select scrub. If it does not lower, the problem is the lift actuator, its fuse, or the lift control, not the brush. If it lowers but the brush still does not spin, continue.
2. Clear the deck. Remove the brush or pad driver. Cut away any wrapped material from the hub and the motor shaft. Spin the motor shaft by hand: it should turn smoothly with a slight cogging feel from the magnets. Grinding or a hard stop means a bearing or gearbox problem.
3. Reset and retry with no brush installed. If the motor now spins freely, the issue was load: debris, too much down pressure, or the wrong pad for the floor. Reinstall and reduce pressure one step.
4. Read the fault. A brush overcurrent message that appears immediately with nothing on the shaft points to a shorted motor or wiring. One that appears after minutes of scrubbing points to load or worn carbon brushes. See brush motor overcurrent faults.
5. Measure voltage at the motor. Reconnect power, lower the deck, select scrub and measure across the motor leads. Full battery voltage at the motor with no rotation means the motor is the problem. No voltage means the fault is upstream: relay, contactor, controller output, or a broken wire, often where the harness flexes as the deck lifts.
6. Inspect carbon brushes. Many brush motors have removable brush caps or a band cover. Carbon brushes typically need replacement when they wear down to roughly a third of their original length or below the wear mark. Worn brushes cause slow, intermittent or no rotation and a burning smell. Check the commutator for deep grooves or burned bars while you are there.
7. Check belts and gearboxes (cylindrical and some disc decks). Look for a broken, glazed or loose belt. A motor that hums or spins while the brush does not is almost always a belt, a sheared key or a stripped hub.
8. Check the brush relay or controller output. If voltage reaches the relay coil but not the motor, the relay or contactor is bad. If there is no output from the controller with no fault displayed, the technician should check it with the service tool.

Symptom, cause, fix

A useful field test: current draw

If you own a DC clamp meter, measure brush motor current while scrubbing. Compare it to the motor rating on the label or in the manual. A motor drawing near its rated current on a normal floor at normal pressure is healthy. One drawing well over rating on a smooth floor at light pressure has internal friction, worn brushes or a failing armature. As a rule of thumb, two identical motors on the same deck should read within about 10 to 15 percent of each other; a bigger gap points to the high reader.

When to call a technician

Call for service when you have voltage at the motor and no rotation and the carbon brushes are fine, when the controller shows no output and no fault, when a gearbox is noisy or leaking, or when the motor shaft is seized. Tell them:

• Model, serial and hour meter.
• Whether one or both brushes are affected.
• Exact fault message and when it appears (instantly or after time).
• Whether the deck lowers, whether the motor hums, and what pad or brush and pressure setting you were using.

Parts that typically fail and rough costs

Many shops replace carbon brushes once or twice before replacing the motor; if the commutator is badly grooved, the motor is usually due.

Prevention

• Sweep or dust mop before scrubbing. Strapping and shrink wrap in warehouses are the top cause of jams; see warehouses and distribution.
• Use the lowest down pressure that cleans. More pressure is the fastest way to trip overload and wear brushes.
• Match the pad to the floor with the pad selector. An aggressive pad on rubber or epoxy can stall a brush.
• Pull the brush or pad driver after each shift, clean the hub, and check it for wrapped material.
• Have carbon brushes inspected at the intervals in your preventive maintenance schedule, commonly every 300 to 500 hours.

Frequently asked questions