My friends have an electric water heater about 10 yrs old. For the past few months when they open a hot faucet after not having used it for half an hour air spurts out with the water which is a scald issue. It's as though air is getting into the tank but we can't figure out how. Any ideas? I thought maybe a bad top thermostat, the water is very hot neither thermostat is turned up very high. I turned them down a bit the other day to see if it made a difference but haven't heard from them whether it did or not.