Gas water heater about 10 years old. Taking warm shower, the water turns real hot suddenly (scalding hot). Turn faucet down and wait (standing back!) - in 30 seconds or so the water gets cooler, so I adjust it back to warm. Same thing happens in a few minutes. The hot water in my sinks gets hotter than usual, but it's not the problem the shower is because one can turn to colder water quicker.