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*** UPDATE ***Three days ago, I was able to successfully pull the T87K Honeywell white round from its base on the wall in the hallway. Just a word of advice - turn OFF any mode switches(T87N) or turn the heat knob setting all the way own(T87K) - before dismounting.
Removing is a hair-raising experience, because it feels like you are literally ripping the thing off the wall! Even if you are slow and deliberate, as one should be in this matter.
Side note: Although not required, I did check the base for level, along the straight edge provided for that purpose. I loosened one of two screws on the base, and ensured it was bubble center.
Here is a link to the manual for the T87K(heat only) and -N(Heat/AC) white round thermostats:
With a tiny standard scredriver, such as the one from an eyeglasses repair kit, one can move these switches to one of four combinations as explained in that subsection.
The third option, both switches 1(top) and 2(bottom) OFF, is the factory default setting.
As installed in our application, I found both dips switched to ON(option #1).
So, I set it to option #2, second down the list, #1 OFF, #2 ON, since it corresponded to the setting recommended for "hot water". Our system by the way is a newly installed hot water boiler, multi-zone (upstairs(us)), and downstairs(two business concerns). Ran it that way for 24 hours, set point 69deg F.
The next day, I removed the thermostat, and configured the switches for option #3, third down the list, OFF/OFF, the aformentioned default. Ran it that way, and continue to as of now 48 hours.
In all three configurations(as I found it, and the two configs. I tried), the difference between set point and actual hallway temperature persisted, with a difference between all three configurations about half a degree.
EG: at 69 degrees setting, an indicated temperature of between 64-65F was maintained. In my apartment, because of our thermopaned windows and weatherstripped(by me) entry door, this equated to 67-68F. Please understand that I already know that the two pointers(set point, and thermometer) will never always match. But while I can understand a 1-2F difference between setpoint and actual, I find a 4 degree difference to be a bit much.
Now: recall that I did mention that the boiler/hot water system in this building is of MULTI-zone design, two floors, two zones. I would assume some sort of thermostat or other regulation exists for the tenants on the ground floor.
For the heating & plumbing experts here: would this application, being multizone, affect or elicit the 3-4 degree F offset I noticed since heating season began here, both before and after the boiler was replaced? I am not well versed in how multi-zone hot water works, having lived most my life in homes with single zone, single thermostat hot water heat.
Thanks for reading this exhausting account of my experimentation, and let me know what you think.