Lennox G40UH Gas Furnace. Burners fail to ignite start.

The other night started blowing cold air. I went to the attic and you could see the furnace cycling ON and OFF every 10 secs, (both LED always flashing green fast, never red), until the unit would shut off after 10-15 mins of cycling. The whole process would repeat all over again once it started getting cold in the house.
People suggested tapping on the tapped on the primary limit switch. It didn't work for me.
Help please


https://www.youtube.com/watch?v=agRy...ature=youtu.be

There is an established process of troubleshooting a furnace and plenty of components that need to be checked in that process.

Check these first, 5 Reasons Why Your Furnace is Not Igniting? | Assured Comfort, after that it's knowledge and skill intensive.

As an example...How to fix LENNOX FURNACE. Burners failed to ignite start. Cleaning igniter flame sensor. Fixing DIY - YouTube

That's just the start as first you need to know how to interpret your furnace codes.