Captaincrunch,

You may be correct in theory, but upon doing a search here for no heat, both of those two situations come up.

1. Aux. water pump failing typically means no/low heat at idle, and good heat going fast.
2. Monovalve bad, typically means good heat at idle, no/low heat going faster down the road.

My wagon was experiencing the latter and I changed out the plunger (monovalve repair kit) last thursday night. She throws more heat out now than a cherry red wood stove.

It worked for me.