I had the same problem not long ago, flame wasn't shooting out the vented tube but it was orange which told me that I had an oxygen depletion somewhere. Thank the Lord these things are mechanically basic, I simply performed the same steps to resolve the issue and things were all good from there.
Just a side not in relation to HW heaters: The one problem I do have is my pilot going out even though the propane is full. To combat this, I figured the problem was one of two things, 1) wind blowing it out or 2) not enough air and the pilot itself starves. So happens to be number two. I can have the HW heater door latched closed while the heater is actually blowing the flame down the tube to heat the water because the flame itself is drawing the air into the heater but with the heater on pilot and the water hot, leaving the door latched starves it of air. To combat this, I don't latch the door it fully closed, I pull the latch through the latch eyelet and then use a pin to keep the door from flopping down but allowing air to travel around the door edge.
Hope that helps others that may be finding the same problem is causing them grief/loss of propane or worse yet, a potentially explosive situation.