The furnace had been working fine.
The next morning, I noticed cold air from the register.
The Main burners were not lighting.
The pilot flame was strong, but yellow.
When I tapped on the gas valve, the pilot shut off
Removed the pilot tube to clear any possible blockage.
Removed and replaced the 3-Wire (used previous sparker)
When everything was back together, switched on the power. The inducer fan ran for 4 minutes.
No spark.
I shut it off the power.
What might this problem be?