Flushing Navien 240A set up for external bypass

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C Steve

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Boston Ma
Flushing Navien 240A set up for external bypass through the furthest HW line
Should I leave the internal 2 way valve set to "ext" (6 OC) and shut off the external bypass valve installed under the water heater at inlet to the bypass pump then proceed flushing through the CW and HW service valves....then after 1 HR vinegar flush just disconnect the CW service valve/open the CW supply and flush?
Should the internal 2 way valve be switched from "ext" (6 OC position) to "int (9 OC position) during the flush and then back to "ext" when flush completed?

Nowhere in the Navien manuals do I find procedure for flushing when set up for external bypass, also nothing on this in many searches in the internet.

PS: See my earlier post (here) reason why I am trying to figure this out.
"Navien tech says to change internal 2 way from "ext" (6 OC) to "internal"(9 OC) during the vinegar flush as they say the flush will clean out the cir pump and internal check valve if the 2 way is set to "int" from "ext" but, this does not make sense to me.

With the CW and HW inlet and outlet valves closed and flushing through the inlet and outlet "service connections" the flush is running through all internals and I expect a DP (differential pressure) drop inlet to outlet.
So....as the outlet pressure from the buffer tank at the inlet of the 2 way internal selector valve is logically less than at the CW inlet flush connection (due to the pressure drop caused by the flow restrictions of the HX and piping) I don't see that there will be any head pressure (higher pressure) available to allow any flow through the 2 way valve, pump, and internal check valve back to the CW inlet flush if the 2 way is set to "int" and maybe even introduce some scale into the bypass pump and internal check valve as well that would not be good?"

Help !

Tx, Steve
Hey, wait a minute.

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