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Hi I'm Brian and I'm here to help!
If this is a Lennox furnace, the 200 error code is a roll-out switch tripped and it will lock out the furnace from firing. A rollout switch detects when the flame from one or more of the furnace's burners has rolled out of the burner tube (venturi). On a new furnace, I would suspect a venting problem with the flue or possibly a poorly installed vent cap and a high wind blowing back in the vent. It could also be a clogged exhaust vent (flue) or gas pressure issue. Other causes are a dirty heat exchanger but that's not likely in your case.
Rollout switches are manual reset. Click Here for a link to a typical one for sale with a good picture of what it looks like. You can see the little red reset button in the middle of it. These are located right near the burner nozzles on your furnace. On high efficiency models, you may have to remove a panel cover over the burner assembly to locate it (them).
Let me know if you have questions about this.