I have a early 1990's Carrier Weathermaker SX furnace, model 58SXA100, with a hard to diagnose problem. Every so often it will fail to start when the tstats call for heat. I have a 3 zone set-up, all of the tstats are new, same model and have been checked for the proper voltage. The circuit board that controls the dampers has also been checked. I've also had the relay board in the furnace replaced recently.

When a tstat calls for heat, I'll hear a "click" on the tstat, but absolutely nothing from the furnace. I've read other issues where the furnace will fire then stop, but this one just does nothing. Only after I hit the CPU reset, or timer reset buttons on the damper motherboard will it start up again and it will run fine after that.

Someone mentioned this could be a draft switch, but if nothing kicks on to start when the tstat calls for heat, is there anything between the tstat and the draft switch in the order of operations that could be causing this?

Did you ever get a answer to this? See it was years ago but I am having that exact problem, same furnace, and am being told I need a new furnace as it is a known problem and the part to fix is no longer available.

Yes, it was the lockout timer/switch gone bad. I wound up replacing the furnace anyway, but the lockout timer was the only thing left that could go bad.