Problem with a gas fireplace?

we just got a new gas fireplace and had to run a copper line to hook it to the gas line. the flame comes on, but it's very small and doesn't put out hardly any heat. is it possible that the plastic accordion - type line that connects the copper line to the fireplace is too narrow? all other appliances in the house (the stove & hot water heater) are all completely lit, it's just the fireplace. does anyone have any suggestions as to what it could be?