No heat in '04 Forester

First check the coolant level. No heater will produce heat if the coolant is low. Also check for an air bubble in the system.

Another easy/no cost check involves feeling the hoses that connect to the heater core. With the engine up to operating temperature, grab the heater hoses under the hood. Both should be too hot to hold onto if coolant is circulating. If both are hot then a problem under the dash somewhere.

My guess is your Subie has consumed or leaked enough coolant to put a air pocket in it. is the res empty? open the rad cap, Is fluid up to the top? yes, then disregard the following. Add coolant to the res, fill the rad full and cap. idle car with it off both defrost settings until A: hot air blows from the blower, b: the cooling fans kick on by themselves. You may need to hold the rpm's at 2000-3000 to get the fans to turn on. When the fans are on, hot air blowing, and the gauge is stable at slightly below 1/2 then you turn off the car, turn the key on and the ac on- this will turn the fans on and cool it, drawing more coolant from the res into the rad.

My guess is your Subie has consumed or leaked enough coolant to put a air pocket in it. is the res empty? open the rad cap, Is fluid up to the top? yes, then disregard the following. Add coolant to the res, fill the rad full and cap. idle car with it off both defrost settings until A: hot air blows from the blower, b: the cooling fans kick on by themselves. You may need to hold the rpm's at 2000-3000 to get the fans to turn on. When the fans are on, hot air blowing, and the gauge is stable at slightly below 1/2 then you turn off the car, turn the key on and the ac on- this will turn the fans on and cool it, drawing more coolant from the res into the rad.