Getting rid of an air lock in the heater feed line(s)

Hello All,

I recently posted about having removed my auxiliary heat pump and rebuilding it. That went quite well, and I did recover my heat, but I decided afterward that I wanted to check something else that I'd overlooked so I removed the pump again.

Now I'm back to having no heat and now the line that leads to the auxiliary heat pump is never getting warm, which suggests to me that I have induced an air lock in these lines after the coolant partially drained out. I was hoping that this might "fix itself" just from the force of coolant being pumped by the water pump, but I'm guessing that the check valve that prevents backflow out of the heater core is effectively preventing that since there's air in front of it.

Any advice as to how I should go about purging the system of air in this area would be very much appreciated. My first thought is to remove the hose that comes out of the auxiliary heat pump and hope that simple gravity will feed enough coolant back through to allow this lock to be broken. However, if someone has definitive advice on how to fix this I'd rather know in advance than keep trying things that might not or will not work.