When I did my water pump, I had no heat in the cab after I was done. Turns out I had an air lock in the heating system. I was like you, I had some heat but I only think it came from the fire-wall being hot in the summer.
CDNSARGUY suggest putting a prestone valve (?) in the heater hose to bleed the air off. So much easier than my method.
I took an old cork from a wine bottle, trimmed it to fit into the long nipple pipe coming from the water pump, so when I removed the heater core hose, I didn't drain off a gallon of rad fluid. I then stuck a funnel in the hose and lifted it up high and poured some rad fluid into the heater core until I felt I had pushed the air out. You'll see the level rise in the radiator. I then dropped the hose and pulled the cork, putting it back together and having a working heater core again.
