06 f550 6.0. with 29000 miles no cab heat at idle. I have checked the coolant for combustion gas found none (does not leak or burn coolant) engine temp runs in normal with new thermostat, changed water pump(pump housing does show wear, I will try to post a picture. egr was deleted with a new oil cooler and coolant flush. I installed a in line pump between the cab heater and water pump which corrected the problem. Im at a loss what to do next.