It sounds like an intermittent problem. If you can reliably reproduce the symptom you or someone else has a chance of fixing this. Otherwise you just clean things and make sure that the connections that could cause this symptom are not corroded.
If it happens every other day on average, then you'd need six consecutive trouble free days to be virtually certain the problem is fixed.
A simple circuit with a few $2 relays from Hosfelt.com could alert you when the problem shows but I'd need a furnace schematic and the sequence of events during startup.
I did something like this to find what turned out to be an intermittently defective clutch relay for my '89 Sentra. It was four LEDs mounted on the dash, each one monitoring a different point in the cranking circuit. As it happened, when I first hooked up the circuit to test it the problem showed up, as indicated by one LED not lighting.