Problem can also be lack of air to the combustion area. Vacuum the area towards the bottom of the tank where the vent holes are. Also, I had a resident that had fans blowing out of her apartment windows this summer. We had the same problem with the pilot light and even replaced the thermocouple. Problem continued and even had CO in the home when the tank was firing. She was creating a back draft and pulling the exhaust gases into the apartment from the hotwater tank. It took time to figure it out.