I have a Hearth and Home HHFPDF32F1. The pilot light will not light. When I press the control knob, it sounds like the gas is sputtering. I’ve checked the valves behind the unit and at the tank, both are fully open. I’ve vacuumed out the unit as well. If I put a lighter to the pilot there is a small blue flame until I remove the lighter, then the flames dies. Any ideas?