Oil side works perfectly on its own.So it is going thru the boiler then?
Yup, one way. Each line has 4 elbows as well so eeek. My local hardware store has 1” pex in White but only 5’ sections. I guess i could tear all this stuff out and stick with 1” to the heat exchangerOne way? I did some quick looking and from what I saw the absolute most you'd flow is maybe 5gpm. That is not taking into account whatever fittings you also are going thru or whatever else might be adding head, just assuming straight pex. One elbow adds about 10' of pipe length. That's a killer on the 3/4.
Silly question - when you're trying to run the OWB without the boil boiler does the return piping on the oil boiler get warm at all? Have you tried running the oil boiler circ at the same time you're running the OWB? Is it possible you've got a check valve at the oil boiler messing with your flow?
The return piping to the OWB does get warm but the return piping on the oil burner does not. I make sure the oil burner circulator is running when the OWB is circulating as well.
Anything at this point could be possible but I do not see a check valve anywhere.
You're correct the OWB return piping is plumbed into the oil boilers pressure relief. I wasn't very sure about this connection but 1 installer and 1 dealer said this would work. There is no other piping coming in or out of that relief valve except the OWB piping.
That smaller diameter copper pipe at the bottom of the oil burner is actually the domestic water feed line to fill/pressurize the system. This is how I back flowed domestic water to my OWB to fill it. This does have a shut off and is currently off.
I don't see anything preventing the OWB from going directing into the oil burner like it is. The only thing I can think of is that the oil burner pressure relief valve is maybe not connected to the oil burner supply/return somehow. I do get hot OWB water from that relief valve if it is opened so Im at a loss.
My two cents - you're narrowing in on root cause here. I still think you should use the flat plate HX, for the record, but I'd bet right now that you've also got a plumbing issue. Is there any reason you can't tie directly into the system return vs using that pressure relief circuit? Depending on the internal plumbing of your oil boiler that pressure circuit could be absolutely worthless. It may well be preventing any flow from your house. It's also not likely sized correctly (internally) to support the flow rates you need.
Don't buy a new pump. Relocate that return line. And install the HX for long term reliability.
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