Best Of
Re: Drip to nowhere.
No evidence there were ever under the floor wet returns. This is the only drip in an otherwise conventional one pipe system.
I have to open up more wall to see where it ends. Being in line with the sink drain raises suspicions.
Re: Missing skim pipe
Side note, this is why i need to get rid of the stanley black and decker stock i inherited.

Re: Faucet brands
I've had superb luck with Chicago Faucets — both original quality, and as some of you may have read, with service. Likewise I've never had any trouble with Moen, although I find that it is necessary to replace the cartridge from time to time — perhaps every ten years — but again, they are very responsive.
I have Kohler single handle faucets for all bathroom lavatories, and I've never had to repair them. The tubs and showers are a rather odd mix…
Years ago I did use Delta, but… something happened and I found them to have short lifespans.
Re: Boiler Running Full Tilt, Cold House
I had a customer with a similar condition. Early munchkin serving a completely uninsulated slab section on S.F. hillside. Pre thermal camera. After much theorizing and measurement I found the smoking gun. Being on a hill there was little question about what way heated water would flow if that was the loss case. After six small holes were drilled in the joint of the driveway below the structure the heat flow was identified. It would have been easier with a thermal camera. Running flat out for 24 hrs will have a loss signature somewhere. The volume of dripping condensate is proof positive of BTU development.

Re: Water line disappearing
1 or 2 pipe? If it’s one pipe, pressure can’t push water out of the boiler.
Depending on the timing it could be surging
Re: Water line disappearing
Is this a one pipe or two pipe system. You say you lowered you dry return. Can you take pictures to show exactly what you did there please?
Re: Boiler Running Full Tilt, Cold House
Shut the water feed off to the boiler. I'm suspecting a leak in the underground. Those Btu's are going somewhere or the software is lying to you. If the pressure drops and boiler shuts down on a water pressure fault or low water cutoff shuts down the boiler then you will know
Re: Missing skim pipe
Just leave the nipple and elbow in place and plug the elbow. Or install a 3/4" or 1/2" valve in the elbow with a bushing.