rotary hammer suddenly has no power, feels weak drilling into concrete, like it's bogging down instantly.

Diagnosis

The sudden loss of power and "bogging down" sensation in the Bosch GBH2-28L is typically caused by a failure in the electrical connection between the motor's armature and the brushes. When carbon brushes wear down past their effective limit (usually below 5mm), the spring tension is no longer sufficient to hold the carbon block firmly against the commutator. This creates a high-resistance gap or intermittent sparking, which prevents the motor from drawing the full current needed to maintain torque under load. If the tool feels weak specifically when drilling into concrete but spins freely in air, the issue could also be a partial failure of the internal grease lubrication or a slipping clutch. However, the most common culprit for an immediate power drop in this specific model is "brush hang-up," where carbon dust builds up inside the brush holder, causing the brush to stick and preventing it from making full contact. You can confirm this by checking for excessive sparking (blue/white flashes) visible through the motor vents during operation.

How to Fix It

To restore full power to your GBH2-28L, follow these precise steps to service the motor brushes:

1. Disconnect the tool from the power source immediately to avoid electrical shock.
2. Locate the two rectangular plastic brush caps situated on opposite sides of the motor housing. Use a small flathead screwdriver to gently pry these caps outward.
3. Using a pair of needle-nose pliers or a magnetic pick-up tool, carefully slide the carbon brushes and their accompanying springs out of the housings.
4. Inspect the length of the carbon blocks. If the carbon is worn down to a nub or is shorter than 5mm, they must be replaced. Use Bosch genuine replacement part number 1 607 001 007.
5. Inspect the commutator (the copper segments on the rotor). If you see heavy black carbon buildup, use a piece of fine-grit sandpaper (400-600 grit) or a lint-free cloth dampened with isopropyl alcohol to gently clean the copper surface.
6. Insert the new brushes. Ensure the spring is seated correctly and that the brush slides smoothly in and out of the holder without binding. If the holder is tight, use compressed air to blow out any accumulated carbon dust.
7. Snap the rectangular caps back into place until they click securely, then perform a test run in a low-resistance material before returning to concrete.

If That Didn't Work

• Check the Power Source: Ensure you are not using a thin-gauge extension cord over 50 feet. The GBH2-28L draws significant amperage; a voltage drop caused by an undersized cord will make the tool feel weak and "bog down" even if the motor is healthy. Switch to a 12-gauge heavy-duty cord.
• Inspect the SDS-Plus Chuck: Check if the drill bit is fully seated and locked. If the bit is slipping within the chuck or the locking mechanism is fouled with concrete dust, the energy from the piston is not being transferred to the bit, creating the illusion of a power loss. Clean the chuck with a wire brush and apply a small amount of SDS grease to the shank.
• Verify the Mode Selector: Ensure the mode selector switch is fully clicked into the "Hammer Drilling" position. If the switch is caught between "Drill" and "Hammer," the internal gear engagement may be partial, leading to a significant loss of torque and erratic power delivery.
• Inspect the Power Cord: Check for internal breaks in the cord, especially near the strain relief where the cable enters the tool. A partially severed wire can limit current flow, preventing the motor from reaching full RPM under load.

Heads Up

• Always apply a small dab of SDS-plus lubricant to the shafts of your bits before insertion to prevent premature wear on the chuck internals.
• Avoid "forcing" the tool into the concrete; let the hammer mechanism do the work. Pushing too hard increases friction and heat, which can accelerate brush wear and overheat the armature.
• Periodically blow out the motor vents with compressed air. Concrete dust is abrasive and conductive; if it accumulates inside the housing, it can cause short circuits or premature brush failure.
• If you notice a burning smell accompanying the power loss, stop immediately. This indicates a winding failure in the armature, which requires a full motor replacement rather than just new brushes.