Hello. I have a furnace that I can hear the following steps:
1. thermostat clicks to turn on furnace
2. the furnace immediately turns on the exhaust fan
3. then I hear a click, and the burner is burning, but only for 5 seconds or so and stops.
4. then another click, and another, etc.
5. the burner kicks on again for 5 seconds or so and stops.
6. then another click, etc.
7. the burner kicks on again and stays on this time.
8. 30 seconds later the blower kicks on and heats the house just fine.

This is the sequence, and the amounts of time it actually burns and stops varies. Sometimes it works perfectly. What could be the problem?

Thanks,
Dan