I have a ~14 yr old Carrier Weathermaker 8000 (58WAV). It turns on and operates normally for 2 to sometimes 15+ minutes, then shuts off prematurely (thermostat still calling for heat). It will attempt a redraft which is sometimes successful, sometimes not. Normally won't show a code, but when does shows 31. Pressure switch appears to be functioning, my guess is intermittent inducer motor operation. Could this be given the symptoms? A $300+ test scenario to replace. Other ideas?