Water heater 15 yrs old & gas. Lose hot water before can fill bathtub. Wait 20-30 minutes, water is REALLY hot, and seems to last longer. Is this a sign to replace, or a symptom of a simpler problem? Solutions?
I have seen those symptoms many times. It often turns out to be a sticking thermostat/gas valve. Especially if it happens after a long, slow cool down… Like over night or a full day without usage. Considering the age of your heater, replacement is probably the most cost effective course of action.