This is a 3 ton single packaged gas unit thats 6 yrs old. Trane YCC036F1MOB model if that helps.
The heart of the problem is something is shutting off the gas valve when the system is trying to heat up. I checked the blowers and they are working fine. When the thermo calls for heat everything seems to be working right all up till it comes time to open the gas valve. I can hear the valve opening and the ignitor lighting. It will burn for a few seconds then shut off. In about another 60 seconds it starts over again. Sometimes it will stay light but sometimes it won't and after several trys it goes into lock out. Could this be a faulty safety switch? The weird thing is it doesn't do this everytime. The only fault code I get on the ign LED indicator is "system lockout"