Atlas to the world --- stay up there I am getting tired
Lets revisit the fact that you are moving energy [stored in the coal] from the conversion source [ the boiler] to your comfort [ the load]
Then let me get you
past the fact that you are NOT pumping water because as above --->you are moving energy
or think of this as circulating energy
so ---you are employing a [ or several] circulator(s) NOT a PUMP
if you were pumping you would be creating pressure and your not creating that - the wet system is UNDER pressure or atmospheres of weight - remember if you have and air bubble in the supply or return line - even just a small one at the top of the pipe loop - your "circulator" will not function because is does not create any
pressure to force the bubble out of blocking the flow it wants to make.
Ok That written ----
Now think of my analogies regarding the similarity of a a vacuum cleaner motor and your circulators = when you plug the vac hose the vac motor does what???? it speeds up right because it is not moving air and it is operating under almost non load.
Take that thought - and apply it to your "new"pump running full out for the first three minutes - SO WHAT??? it is simply moving or circulating as much energy bearing liquid in relation to the number of open zone valves - if only one zone valve is open at the time - the circulator is not creating a tsunami into that zone --- so it runs for three minutes and then begins to process - It has to because if it didn't purge the zone it would be running forever too slow to satisfy the zone - it has to see a correct return temperature before it can supply a correct supply temp
Think of the work the circulator is doing in regard to System Balance of improper installed loops and choking flow on the SUPPLY side of the circulator - if you choke too much all that happens is the load will not see any energy bearing liquid and the pump runs happy ever after - under almost NO load.
your "circulator' works as necessary to supply one or all demands - is works [ if you could measure amp draw ] - up to demand - and only loafs when demand is low - This appears to be the opposite of what i think your thinking
but then what was I thinking when I started writing all this drivel - try this circulator on for size once and see if it chafes???