If the temp gage barely moves, you’re not gong to get hot air out of the heater system. First you need to figure out why your engine isn;t warming up and correct that.
Possible cause of an engine not heating up are
- a stuck T-stat (I did notice that yyou already changed that)
- low coolant (see CSA’s question)…did your purge the system?
- extreme winter temps…like we had in ND when I lived there. We had to upt carrdboard in front of our radiators to get the engines to warm up. Where do you live?
Also, if when you purged the system you did not have the heat on, you’ll still likely have air in the heater core. You need to turn the heat on to open the valve that allows the coolant to flow through the core (and purge the air) on many cars.
Unless you had some other reason for changing the water pump (?), that would not be expected to help. It is good, however, that you found that pinhole.