My intertherm furnace keeps turning off after about 6 seconds. It'll be off for about a minute then will burn again for six seconds and stop. This keeps repeating.

Try checking your plug. Can it be upside down? That is commonly caused by reversed polarity. If it's a new install they could have wired it backward. The other issue could be that one burner may not be firing, or the safety sensor that senses the flame could be bad. But don't clean the sensor. It is delicate and if cleaned improperly will make it fail.