Also clean the front grill and try running it without the concentrator/diffuser - backpressure and residue on the heater cage will make the thermostat trip early. If your plug has a TEST/RESET press reset and use a short direct outlet run on high fan with low–medium heat, and pulse the cool-shot to keep the cutout happy but then... if it still overheats after a thorough clean, the thermal fuse/thermostat is likely weakening or the motor is dragging, which isn’t user-serviceable, so push for a return or warranty.
One more thing to rule out is motion blur masquerading as bad autofocus - kids move so try shutter speeds around 1/250–1/500 and raise ISO or add light; stabilization helps your hands but won’t freeze the subject. For grandkids, use continuous AF (AF-C/AI-Servo) with a single focus point on the face and enable the AF assist lamp and focus priority. Also try a different lens and reseat the current one; if another lens focuses fine, you’re likely looking at a lens-specific calibration that AF fine-tune or a service can fix.
