2001 Chevy s10 with no heat

If you are certain there is no air in the coolant system, then there is a chance that the blend door motor is not working or the heater control assembly is bad. since you have replaced your own heater core you probably noticed the the doors inside the heater core housing. One of those doors is controlled by the "hot/cold" knob. The motor on that door could bad.

Turn on your heat and touch the hoses that enter the heater core see if they are hot going in and coming out if they are hot it could be that your blend door for hot and cold is not working that is under the dash on the pass. side.

I have had this problem of no heat with my 94 S10. I have flow through my heater core ( both intake and return lines are hot ) and still no heat ! I figured out how to fix this ! If you have tryed everything or before you spend and money...eg: replace heater core, thermostat, flush ect... try the switch/dial where the hot/cold button is ! THIS IS HOW YOU FIX IT ! my switch was arced out and hence it could not acknowlege itself to turn on the heat ! Take the switch apart. If you see black burned stuff you need a new one. Bend back the four bendable tabs and look at the inside. If it is full of grey oxidization clean it with some rubbing alcohol until shiny. I know this is the answer if all else fails and cleaning or replacing a dial switch is a cheap alternative to other parts ! Good luck ! :) Doucette

CHEVY HEATER PROBLEM RESOLVED IN A FEW MINUTES COSTING LESS THAN $50.
My 2001 S10 Extreme 4.3Ltr had the SAME 'No Heat' Issue.
First with the engine running and the heater in the on position set to hot, I acknowledged that the heater hose coming from the block was warm, while the hose coming from the heater going to the water pump was cold, meaning blockage.
I then went to the parts store and purchased a cooling system flush and the flush kit, and then followed the instructions.
Basically speaking the cooling system usually builds up a blockage {like a blood clot} at the very small orifice that leads from the block to the heater {heater hose connection tube}.
Following the instructions, Flush the system and then replenish the coolant. WALLA!

I had the same problem with my 1999 s10....my mechanic replaced a part that i cant remeber the name of but it was only $20 and a 2 second installation....i can send you a pic of the part if your still having the problem.

Change the thermostat to a winter temperature one. ... if you are getting no heat at all there is a possibilty that there is a blockage in one of the hoses as well or air in the system... are the vents even working properly ?

Robert