I am new to this forum so please forgive me if I am bringing up an issue that has already been posted. I am interested in some feedback on a problem furnace.
I have a Trane EX80 system that is about 14 years old. The problem is that the furnace eventually locks out (no fire indicator) and blows cold air. This is an intermittent problem although it is gradually becoming more prevalent. My first thought was to clean the flame sensor, which I did. I then replace it with a new one but the problem is still there.
Here are the systems: The sequence starts with a call for heat, the draft fan kicks in, the igniter glows, and the gas starts and ignites. Then instead of continuing to burn, the flame goes out for no apparent reason (the time it take before this happens varies greatly). The furnace then tries to restart the flame, that is the ignore glows and the gas will try to start; however, sometime the gas turns on/off in such a quick cycle that there is no way it could ignite. It acts like the sequencing for the light off and sensing of the flame are out of sequence. After about three or so tries to ignite the furnace then locks out.
I am hoping someone might have some suggestions for troubleshooting this problem.
Sorry for the delay. I did check the pressure switch and it was functioning fine. I also spotted some additional indicators in the process. The faulty light never indicated and faults before locking out. One the call for heat was dropped (i.e. physically disconnected the wire) the furnace remained in a call for heat state until locking out. I ended up changing the Control board and it works great now. Thanks for you input.