Boiler is hotter than leaving water temp,

Russ Q

I have a recent boiler installation that has a problem with temperature in front of boiler is 40 to 45 degrees hotter than the temperature leaving the back of the boiler, return water temp is 135, leaving water is only 142 but thermometer in front section is reading 180-185. Per mfg. instructions both return and supply pipes enter rear section and boilers included a 2-1/2" "water balancing tube" that wes installed in the bottom tapping of the boiler on the return piping. these are two DeDietrich GT308A/II 8 section boilers max btu=1.2mill with oil fired Riello burners and a closed loop with 40% propylene glycol. Each bioler has its own pump moving 65 to 70 GPM into the boiler then back into a primary HW loop that has 3 secondary HW loops feeding the building.
I suspect that boiler flow is "short cycling" through rear sections and not inducing flow in the front sections but not sure if glycol might be foaming in boiler and "stacking" in the front sections preventing heat transfer from the boiler to water? I'm looking for any other ideas you may have? Have you encountered this situation in the past? I am attaching a copy of the I&O instructions.

Steamhead (in transit)

They're probably under-pumped

if a circ is moving 65 GPM, it can only move 650,000 BTU per hour. Those boilers' gross output is 990,000 each, you'd need 99 GPM on each boiler and maybe a bit more for the glycol.

What circs are you using on the boiler loops? The B&G 2-1/2" circ approaches 100 GPM at about 4-1/2 feet of head........

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bluenose_33

Circ

Are you sure the circs are not pumping into the supply and trying to get out of the return?Just a thought because its a fairly new install.

RonWHC

Is the correct

water balance tube installed?