Circulator pump location

The boiler I'm working on has the circulator on the outlet of the boiler, essentially pushing the water through the heaters rather than pulling it.
Is this ever legit?

I've never seen it this way, but don't know why not.

It's totally legit (preferred, in fact), so long as the expansion tank & air scoop is between the boiler and the pump.



Books have been written advocating that system architecture. It's nicer to the pump, and allows the air scoop to purge air somewhat better than some other configurations.

On some low mass boilers (particularly those with higher head) it's sometimes better to pump toward the boiler making it the high-pressure point on the system to reduce flash-boil sizzle to not lose heat-transfer efficiency.

More here.

Curious.
Almost every one I've ever worked on had it as the very last thing in the line.
I always assumed is was so in case of a break, it would suck in air rather than pump out water and run the boiler dry.

Unfortunately, this one is before the expansion tank, so I suppose I'll be moving it.

All boilers today have low pressure cutouts that shut them down with an uncompensated leak. A circulator run dry will fail fairly quickly, at least most of them use the water to lubricate their bearings. Having the expansion tank before the pump helps to ensure the pump stays full of water and not create microbubbles or water flashing to steam.

Nice drawing Dana! All low-mass boilers, including electric boilers, should be pumped-to for the reasons mentioned. It is the position of the expansion tank and air-eliminator that is most important, most properly, always on the low pressure side of the pump. This maintained the point of no pressure change.