I've had my ED for about 15 months now. It has only 48K miles. My heater has stopped working consistently. The unit will provide heat for the first 10 minutes in manual control. If I switch to auto control, it will only blow cold air with temp setting significantly higher than cab temp. If I take the control back to manual, it too blow cold air. No matter what I change, I can't get the unit to blow hot air. It has been raining here the last couple days so the temp sensor is not getting warmed from the sun. The hoses are hot heading through the fire wall. Any suggestions?