Why does the boiler manufacturer show it this way?
I think the title says it all. I don't get what this bypass is for.
The idea is to slow the onslaught of cool return water through the boiler so it could pick-up the burners heat without condensing, while still maintaining an adequate flow on the system side.
Wouldn't it be better to pipe a portion of hot water leaving the boiler, back thru the return?
Can’t say, it will be better, complete system-side flow would suffer that way IMO.
So you think this way is better. I guess it is the manufacturer's instructions.
Not to hijack this post but I was just about to ask the same question for the same reason. I thought the bypass was piped wrong and was ready to change it after I checked here first. Now it makes sense.