You are absolutely right Yanche. But at 150-160 degrees the water has already lost its air for the most part and will not entrain it even in a vented feed tank. The only new air will be in tiny amounts when the PRV adds a tad of water to the system to maintain pressure. I feel this is easily exceptable. I do not want my pump seeing the high temps that I get from my boiler's output, as it has gone 240* and more a few times. To me, the pump life is more important than the bubbles.
This is why I stated the gas/oil vs. solid fuel earlier. The gas/oil will always shut down at the limit setting, while the solid fuel will overshoot it's limits at times and that beats up the pump.
By the way, the pumps temp limit is 240*, that doesn't mean I want it to operate at it.
http://www.pexsupply.com/product_dtl.as ... co&cID=289
Greg may be on to something with the new spec ($$$$$$$$$$$).