Thank you for asking your question on Just Answer. This is a dangerous condition known as flame roll out. It is normally caused by lack of service on the furnace.
Many homeowners do not realize, the complications of not having a professional inspect the heating system yearly, can cause. If a fire, or worse, is caused by the furnace and there are no records of the furnace being maintained, the insurance company can and will deny the claim for damages. I have worked on systems after they have caught fire and the homeowners got no help from their homeowners insurance for the damage. I have installed furnaces in new homes that the owners were building to replace a home that was destroyed by fire from not having the furnace serviced. I like every customer to have this information to consider before repairing the furnace themselves.
You should not continue to use the furnace until the problem is corrected. Doing so will subject the furnace to fire. The burners are most likely dirty or the exhaust vent is blocked. The burners will have to be removed and cleaned. The fire box should also be cleaned as should the other parts of the furnace.
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