For the past year, my CLS has had heating issues. I first replaced the heater control valve since that was what every forum that Ive read said fixes the no heat issue. Once I replaced, the heat did work but after running the car for about 15 mins, the heat will stop working. If i start the car from a cold start, the heat will work. If I shut the car off after warming up and restart and try to use the heat, it will not blow any heat. Where should I look next? I am stumped. Im thinking possibly the thermostat is going bad and somehow ties into this system.