Ford Repair: Ford f150 with 4.2 engine, heater control valve, coolant level

Question
I have been having trouble getting the heater to throw hot air in my truck. I have replaced the thermostat, water pump, flushed the system...I have noticed a gas smell in the coolant, what might this be?

Answer
I have to assume that it is around a 2000 year model? You didn't state the year model. A faulty heater control valve would cause the heater to stop working, as well as a low coolant level. As far as gas in the coolant, you may be looking at a gasket failure. Either the intake gasket, or head gasket.