2010 Prius no heat and slow coolant leak problem

It is starting to get cold out (upper 30's) and I've noticed I don't get more than luke warm air in the cabin, even after 30 minutes at full heat driving. The car drives fine with no warning lights, getting 55mpg. I tried some grille blocking with no effect. I checked the coolant level and it was below LOW, so refilled it. That didn't have an affect. I suspect I have a slow leak and that the heater core is either clogged or the pump to it is not working. I do not know the location of the core or I'd feel the in/out lines to see if one or both are hot after use. I'd like to address that issue and then the leak (if separate). Note: I did buy this used 6 months ago and had to fill coolant then too, but I found a cracked hose that I replaced and I thought that was the only leak at the time.

 

If it were the head gasket, that would not explain the heating problem, right? Any ideas on how the heater core is or how I can check that? I'll check for frothing bubbles in the radiator with cap off and engine running.

 

I'll try that Chap. I have a bluetooth OBDII adapter and will find an app or check with my friend who has Techstream I did completely drain coolant and refilled today, remembering to open the air bleeder valve during refill. Still not getting hot air, so not likely a bubble issue. I also felt the two coolant tubes going into the firewall at the back of the engine compartment (behind bleeder valve) after running engine for 20 min in maintenance mode. Both were hot, so I think the hot coolant is getting into and out of the heater core. Maybe the damper you mention is exactly the problem. I also noticed that the radiator fan never went on during the 20mins I had the engine running. I have no codes.