For the last two nights (very cold weather) our Bryant Furnace appears to be attempting to start, fan kicks in and the burners ignite then it shuts off 2-3 seconds later this happens repeatedly. The first night (around 3 am) I noticed this I turned the heat off with the thermostat and left it for 30 minutes then turned it back on, saw a steady red light on the furnace and it seemed to be working fine.

The second night (around 5 am) I noticed the furnace failing to cycle through again I did the same thing and it seems to be working fine still.

After the first night I cleaned out the furnace with a shop vac to ensure it was very clean, visually inspected the flame sensor (which appeared clean) and thought that fixed it but then it happened again. Should I try to clean the flame sensor with sand paper? What else should I check?

Yes, your first move should be to remove the flame senser and clean it with very fine sand paper, sand cloth, or steel wool, until it looks as shiny as new. Reinstall, and let us know how it works.

Try this first, then post back if problem still exist. Good luck.

You shouldn't use sandpaper because it has silicon on it which can be transferred to your sensor. You should always use steel wool to clean your flame sensors.

Never, ever had a problem with emery cloth(sand cloth). Never actually used sand paper, so you may be correct. Can you post some data to prove this(not doubting that sand paper has silicone, just that the silicone in the sand paper would cause a problem.).
I will guarantee that emory cloth works just as well as steel wool. It states using emery cloth or steel wool in many furnace service manuals.

drewke76. I have heard somewhere before not to use sand paper(due to silicone), but I guess it never really sunk in, till you mentioned it here. Thanks for bringing it up. Never seen a furnace service manual suggest using actuall sand paper, so, like I said, you may be correct. There is a member here(hvac1000) that may be able to clear this up for me. Ive suggested using fine sand paper, sand cloth(emory cloth) or steel wool many times on this site. I just want someone to clarify that using sand paper is not a good idea, personally , I use nothing but emory cloth, just because I have it handy, plumber being my first trade. If I can get some hard facts about the sand paper, I can use it to better myself as a tech. Thanks again for bringing this up.