tool gets super hot really fast, even on light duty, and smells like hot electronics.

Diagnosis

The overheating and "burnt electronics" smell in the Bosch GBH2-28L typically stem from a failure in the thermal management system or a critical electrical breakdown within the armature. When the tool heats up rapidly under light loads, it indicates that the motor is drawing excessive current (amperage) or that the internal cooling fan is no longer moving sufficient cubic feet of air per minute (CFM) to dissipate the heat generated by the copper windings. The specific smell of hot electronics usually points to one of two things: the varnish on the armature windings is beginning to degrade due to heat, or the carbon brushes are sparking excessively (arcing) due to a contaminated commutator. If the air intake vents on the rear housing are clogged with concrete dust, the internal fan creates a vacuum but cannot pull in fresh air, causing the motor temperature to spike within seconds of trigger activation. You can confirm this by checking for a "stale" heat coming from the rear vents and observing if the tool's internal thermal overload switch trips, shutting the tool down completely until it cools.

How to Fix It

To resolve the overheating and clear the electronic smell, follow these precision steps to restore airflow and electrical efficiency:

1. Disconnect the tool from the power source immediately to prevent further winding damage.
2. Use a high-pressure compressed air nozzle (at least 90 PSI) to blow air into the rear intake vents. Direct the air specifically toward the motor housing, blowing from the front of the tool toward the back to push accumulated concrete particulates out of the motor casing.
3. Remove the four screws securing the rear motor housing cover. Carefully slide the housing back to expose the armature and the cooling fan.
4. Inspect the plastic cooling fan blades attached to the armature shaft. Check for any cracked blades or accumulated "cake" of dust on the edges of the fins. Use a stiff nylon brush to scrub the blades clean; any imbalance or blockage here reduces cooling efficiency by up to 40%.
5. Inspect the commutator (the copper segments on the armature). If you see black carbon buildup in the grooves between the segments, use a fine-grit abrasive pad or a dedicated commutator stone to gently clean the surface until the copper shines.
6. Check the carbon brushes for wear. If the brushes are worn down to less than 6mm in length, they will cause erratic electrical contact and overheating. Replace them with genuine Bosch replacement brushes to ensure proper tension against the commutator.
7. Reassemble the housing, ensuring the gaskets are seated properly so that air is forced through the motor and not leaking out of the seams.

If That Didn't Work

• Replace the Armature: If the smell persists and the tool still runs hot, the internal insulation of the armature windings has likely suffered "thermal breakdown." Once the varnish melts, internal shorts occur, causing the motor to run hot regardless of the load. You will need to replace the entire armature assembly.
• Check the Gearbox Lubrication: A dry or contaminated grease pack in the gear housing creates massive mechanical resistance. This forces the motor to work twice as hard to turn the chuck, leading to rapid overheating. Open the gear case and replace the old grease with high-temp lithium-based rotary hammer grease.
• Inspect the Power Cord and Trigger Switch: A partially frayed cord or a corroded trigger switch can create high electrical resistance. This resistance manifests as heat at the point of failure and can cause the motor to run "lean," leading to overheating. Test the tool with a multimeter to ensure full voltage is reaching the motor.
• Verify SDS-Plus Bit Fit: Ensure you are using high-quality SDS-plus bits. A warped or improperly seated bit can cause the piston to bind slightly, increasing the torque load on the motor and causing it to overheat during light drilling.

Heads Up

• Dust Management: Concrete dust is conductive and abrasive. Always blow out the motor vents every 4-8 hours of heavy use to prevent the "baked-on" dust that leads to motor failure.
• Avoid "Trigger Riding": Do not hold the trigger halfway to control speed; this increases current flow to the motor without providing the cooling airflow associated with full-speed operation.
• Cool-Down Periods: If the tool feels hot to the touch, let it idle at full speed (without drilling) for 30 seconds to allow the fan to flush out the heat before shutting it off completely.
• Voltage Stability: Avoid using long, thin extension cords (over 50 feet) with a gauge higher than 12 AWG. Voltage drops cause the motor to draw more amps, which generates significantly more heat.