Season the chicken with the salt and pepper and arrange the carrots and onion in a 6-quart slow cooker.
Set the chicken in one layer over the vegetables.
Whisk the maple syrup, mustard, vinegar, Worcestershire and thyme and pour it evenly over the chicken.
Cover and cook on low until the thighs reach 175°F and the carrots are tender, 3 1/2 to 4 hours.
Move the chicken and vegetables to a platter and switch the cooker to high.
Whisk the cornstarch with the cold water, stir it into the sauce and cook uncovered until lightly thickened, 8 to 10 minutes.
Spoon the sharp maple sauce over the chicken and carrots.