Gasifier said:
Can the second 007 that should be pumping water from storage at that point be sucking water past the IFC of the first pump and taking water out of the boiler?
In general not a problem, which is good because so many are set up that way.
If you look at the 'Simplest' it's an example of where there's a tee at the top and at the bottom of storage. Load draws from one side and boiler fills from the other, nothing can go wrong because load will pull hot water from storage before it will pull any cold water up out of the boiler and through the resistance of all the extra pipe going over to the boiler.
Now move the connection point for the load side away from the top of storage, further and further towards the boiler. If the piping over to the boiler is long and thin enough, at some point there will be some parallel flow through the boiler even though the water in storage is hotter and lighter.
Throw in the IFC and it would have to be a pretty unusual situation before you'd have to worry about it.
But with the return temperature protection mixing valve there can't be a problem in any event because as soon as it sees water less than its setpont on the 'C' port it will shut down any flow from the bottom of storage through the boiler.