no heat on 1998 Chevrolet Blazer

I have replaced heater core, I can hear water flow thru heater core when i give it gas, replaced radiator cap because i could remove it with no pressure on it but still no heat, radiator is full

Asked by for the 1998 Chevrolet Blazer
maybe recheck for an air lock. i have the same truck and you may have to let it run for a very long time.
thanks replaced thermastat and let it run for awhile fixed it.