The pilot light on our wall mounted propane heater is flickering and too high.?

We have a wall mounted propane heater. It's been flickering like there is air in the lines and it won't "come down" onto the thermacouple. So, therefore we cannot get the panels to light. My husband worked with it for several hours last week and it worked until today. We've been trying to get the panels to light all day. The pilot light is like standing straight up and up highter than usual and not coming over to the thermacouple. We've been holding down the pilot on to try and gt air out of the lines. What next?