Why would the heater in a 1996 Blazer make the cab smell like hot water even after having the system flushed with a new thermostat and new radiator cap?

You have a bad heater core the heater core is a small radiator type unit under the dash of your car that sends hot water from the cooling system runs through a fan blows on it and warm air comes out. It is in the cab under the dash and it is leaking that why you smell "hot water" You need a experienced mechanic or get a book Chiltons if you what to fix it yourself