Do I need to see a doctor if the blister on my heel won't heal?

Yes. Please see a doctor. While you don't mention how long it has been since your blister started and how long it has been that it has not healed, it is always important to know that things that don't heal right, especially on your hands and feet, are things that should be seen by a doctor. Other factors that would contribute to not healing appropriately need to be discussed with your doctor so that he or she can take steps to make sure that the area doesn't become worse or even spread to other parts of the body. While this is obviously a "worst case" scenario, these are the kinds of things that doctors can see regularly, and so appropriate treatment is important in the early stages. All of the years of late nights and little pay that doctors put in during training is so that they can recognize when something is serious and take the appropriate steps to fix it. People who have diabetes, smoke, have heart disease, or other medical conditions are at increased risk of having non-healing sores on their extremities because the blood supply can be compromised. Without enough blood, the healing process is limited. Please speak to your doctor.