Thank you z22! My 2004 MDX had the exact same problem - rear heater was operating fine but no front heat (all fans functional). I used a quality #2 phillips head and cranked down the valve stem screw on the hot water control valve. It turned maybe 1 full turn, but it did the trick! Luckily the screw was not stripped like yours, so I'm hopeful this fix will hold. The odd thing was that my hot water control valve and control cable looked to be in slightly different locations than shown in the posted photo. Nevertheless, the fix worked and I'm greatful for you sharing your experience - saved me some $$$!