2003 crv. Great little car we have had since 2006. Last couple years have had poor heat with setting at top. It always used to cook you out. Have flushed and back flushed the heater core and it has good flow. The hot hose is very hot and the return hose is cool with fan running full blast and temp set high. The temp of the air flow gets less as it runs. Have had hoses and valve off and no restrictions. Pulling supply hose off before the valve and running engine and rad full there is very little flow coming out of block. Flushed both directions thru both heater hose connections on engine. No change and like the heater core the flow thru looked fine on the first application of hose flush. This vehicle corroded a hole in the throttle body coolant passages that actually let coolant into the throat of the throttle body and caused symptoms of what I thought at the time was a head gskt leak. Stopped the leak with some really good head gskt leak repair, not bars leak. Finally got car home from Phoenix and discovered where the leak was and replaced the throttle body, car had shown up with surging idle that was caused by coolant getting into the idle air bypass valve and causing it to seize up. The corroded coolant passage thru the throttle body was completely blocked off by the sealer. So i was starting to think that the block seal may have caused the heater core to plug except that the lack of heat was well before the TB problem. Plus i have just flushed everything in sight. The T stat is good as the coolant gets up to temperature fine. Have looked thru all 3 heater hose pieces and the walls are good so nothing collapsing. It is odd how the return hose from core is plumbed into either the water pump or the lower T stat housing. And that the upper coolant housing that the upper rad hose connects to has a 5/8 inch hose plumbed from it to the “water pump backside under the intake manifold. Any ideas. I have been pulling wrenches and running a repair shop for almost 50 years now and am not used to being stumped. I ;understand air can be a problem so am making sure its all bled out and confirm it by feeling the steel coolant line that goes around the PCV air inlet into the cam/valve cover. Haven’t tried specifically the jacked up front to bleed air. Hopefully no one suggests a weak water pump. They either work or they don’t. In 50 years have only ever seen one water pump impeller come loose from the shaft and its symptom was major overheat.