Best Of

Following up, I have a workable solution for now. If I really choke down the garage baseboard, I can keep the 1st floor living and 2nd Floor west loops from reversing. It's not ideal because the garage baseboard isn't heating up nearly as much as before but for now it won't freeze up and everything else works properly.

The baseboard in the garage is cast iron and made by slant fin. I think it's their "Rhino Cast". I found some install instructions and it looks like the supply and returns should be on the bottom fitting on opposite sides from each other, although I am not sure if it would work just a well going into one top fitting and out the bottom fitting on the opposite side. The bleeder valve goes on the return end upper fitting of course.

Anyways, I appreciate all the help so far. I'm going to eventually make the changes to the mixing valve and rework the garage piping. I'll probably lower the radiator to the ground at the same time. I do think that my idea of cutting the garage return pipe off before the tee with the radiant floor return and connecting it in with 1/2 piping to the return stack at the bottom will improve / solve the issue. If not then it's time for check valves. Replumbing the supply and return stacks to a larger diameter 1 1/4 isn't a practical solution.

PS, Naviclean is clean and unblocked; I checked it.

Thanks for the commentary…

Regarding water level "does not look too high" - I was trying to say it is not above the water level mark on the side of the boiler enclosure when the hammering occurs. During the non-heating cycle the level typically is somewhat below this line by several inches (like the pic above where you are seeing evidence of oil), though several times I have seen it resting above the water level mark. During heating the level fluctuates less than one inch a couple of times or so per second. It doesn't appear to me to be violent fluctuation (i.e., no water splashing in the gauge) but I am a novice at this. My boiler tech told me it is to be expected during heating. This behavior is very similar now as it was with the old piping. Boiler is early '90s, though I can't vouch for how the earlier owners took care of it.

Drain cycle: 2 different boiler techs have told me a weekly drain until the low water switch activates is a good thing, and I have also read it is a good thing. However I have also read about dangers of too much fresh water addition. Reading more carefully I see a probe-type switch mainly needs a yearly cleaning, and this McDonnell switch seems to be just that. So I will have to interrogate the tech about that next time I talk to him.

Best regards, Steve

There is a huge difference between an 007 and an 0010, but if you already had an 007 doing okay for 20 years, it's probably okay. With that said, short cycling using that tank still indicates a lack of heat transfer which could be a dirty exchanger an air bubble, or several other possibilities.