We use a compressor to test the plumbing and also to test the heating ( radiators) line.

Landlord thinks the leak comes from the area by the radiator that isn't covered with the ceramic tile like the rest of the bathroom is [see pic].

This is a 4/2 house and the copper parts on the boiler and every radiator were stolen too.

Will be painting the flashing on the big unit the color of the siding so that it blends in better.Lowered ceiling in kitchen, note wall built out in left corner, radiator will go here, refrigerator will go on the other side in same corner.

The second and third floors, we tapped into the existing piping and cast iron radiators located in their units from the basement.

The pipes/radiators have frozen and the boiler is shot, otherwise it looks to be in good condition.

We had the utility company come out and find there was nothing wrong with the boiler, we've had the plumber come out and bleed the radiator, our contractor insulated the windows and doors on the first floor, and we even bought the tenant a $200 "Amish fireplace" room heater.

Besides the regular DWV plumbing, the house has hot water heat, so those pipes and radiators could've been damaged as well, potentially causing HUGE amounts of damage.

And the overhead with radiator heat (i.e. no way to regulate zones in a 4,000 sq ft converted mansion of 12-14 units) would be enough to ruin most people after a winter like the one we just had. 

Radiator burst two years ago on upper level.