If you are already getting heated water then there is no problem with the heating element. If I understand that you are getting hot water for a full 30 minutes, then you are doing great. I am surprised that hot water would last that long. If so, then you do not have a problem and there is nothing to do. However, if you mean that after using hot water you then have to wait for 30 minutes, that also would not be a problem. I had the same thing happen to me today. I think that when it reaches a certain temperature it shuts off, or it has to wait until sufficient water is in the tank. In my case, I had to manually re-start the heater because I got impatient and did not want to wait for it to re-ignite by itself.