Should I replace my Heater Core? on 2004 Honda Civic

So my windows started fogging up on my recently, my temp gauges are normal, I see no leaking inside the car anywhere, and the heat and AC work just fine. DO i need to replace my heater core or just have it flushed? Or is it something else entirely?

It should be noted that I have heard a bubbling/gurgling noise for over a year come from behind the dashboard when I turn on/off or at stop but not always consistently. This may or may not be related but you tell me. Thanks!

2 answers 2 comments
if temp gauge are normal, no leak and no smell of coolant inside below the heater core, coolant tank level is normal i would not replace heater core, i would recommend to flush the coolant if not done in 3 yrs.
Okay, thanks but what about the bubbling noise i hear, is that normal?
possible air pocket in cooling system...
is that something I should fix or be concerned about?