1998 chrysler concorde LXI HEATER WORKS ONLY WHEN THE CAR IS MOVING WHAT CAUSE THIS PROBLEM
Check the coolant level. The water pump might be worn or the idle RPM's are too low.
If above checks out ok. Check for vacuum leaks going to the flaps of the heater air duck work. At an idle might not have enough vacuum to hold flaps open for heater to blow properly. But while driving you create more vacuum so the flaps can still work even if there is a small vacuum leak. Hope this helps