The fire in the furnace goes/off over and over. The house won't heat-up
enough before the furnace shut down. I did replace the thermostat, but the
problem still exist. I can see the big white fire light-up. Then it goes
down to a blue flame. Seconds later, the blue flames disappear and the big
white fire lights-up again. The house can never warm-up like this. Does
anyone know what could be wrong?

Thanks,
Al