I have a carrier gas furnace, model number 58dhc. Power, blower works properly as far as I know. When I turn the heater on it just spits out air. Hvac repairman suggested replacing a control board which I have done and when heat is turned on after the initial replacement worked for a bit. Shortly there after it stopped working again. Second repairman diagnose the problem to be leaky and rusty pipes that is the source of problem. Went out and purchased new pipes and installed the sections where there are holes, rust. The problem still exist. Everything seems to work except that it will not ignite. Would greatly appreciate feedback and help.

It sounds like you could have dirt in the gas valve from the bad pipes among other problems. Remove it and check the screen then use an ohm meter to check the coil(s) in the gas valve. I would think it would have a resistance of a few kilo-ohms. After you put it back together make sure you are getting 24-30 volts at the gas valve. Some have two coils: one to open the valve for the pilot to light and one to open the main gas valve. Make sure you check both and it has to have a way to prove the flame. Some have a sensor that measures resistance to ground and if it is dirty it will not allow the main gas valve to open and will shut off both valves because it thinks the gas did not ignite. See what you find and let me know. One other thing: Did you put a trap in the gas line before the gas valve? That is a capped piece of pipe about 6-10 inches long pointing down to catch any trash or moisture in line. DrTom4444