I am so frustrated! I do not think my bathtubs were installed correctly. I run hot water into the tub and by the time I sit in it, the water has become bone-cold (especially on chilly nights). We have a large water heater, and the water that comes out of the tap is H-O-T. The shower/tub combo is on a slab foundation, and I don't think it was insulated correctly. Does anyone have any suggestions?