Yep. Clear analysis, clear way forward. Only thing, I have to get somebody to translate to lady #2. I can do that. I don't even have to buy the thermometers. Thanks very much!

There are probably supply and return pipes for each apartment. The temp should be checked after the individual zones have been running for a few minutes, at least. You can use yours as a reference rather than trying to deal with the language barrier in the other top floor apartment.

Scope out the pipes to the problem apartment and your units. Set both thermostats significantly higher than the current temperature. After 15 minutes, go down and check the pipes with your hand again. Ideally, you'd use an infrared thermometer. Inexpensive models can be had for $30-40 that will be adequate. You can also tape an instant-read thermometer to the pipes and insulate it with some rags or something else that his handy.

The the supply pipes for both zones should be identical. The return temps should also be similar and, of course lower than the supplies. The actual temperatures depend on the type of boiler and other aspects of the system (type of radiators or other heat-emitting devices used in your systems.)

It is remotely possible that you have a one-pipe system. That is out of my area of knowledge, but I can direct you to some fora where you can find help.

Good luck

Thank you. When you said, instant read thermometer, did you mean like a meat or a candy thermometer? Would you tell me how to interpret the data I get from taking the temperature? Like, if hers is lower, either on the out-going or on the return, what does that mean about what must be done? I know there's one pipe going out, the return pipe may be elsewhere. I'll look. Thank you so much!

https://www.oxo.com/instant-read-thermometer-480

To make sure it works right, check it with a pot of boiling water. It should read 212 F at sea level. For starters, just feel with your hands again. If there is a gross difference, you'll know that you need to call an expert or get more advice without the thermometer. The the supply pipes for both zones should be identical. The return temps should also be similar and, of course lower than the supplies. Get some data and post back.

Hi! I'm nor sure what you meant about feeling with my hands--that is, what was I feeling? Bear in mind I've had a hundred conversations today about the problem and my head is spinning. But I can post the progress right now. I don't really have to compare the two apartments to see if the complaining person's cold is not related to the furnace but to a need for more insulation, including sealing the windows. In fact, after my request (although he has forbidden me to 'bother him' over these kinds of issues) the old HOA's president shared that two years ago he'd called a furnace technician to say that they had determined the unit did indeed have an actual problem related to a bent or obstructed pipe. The solution had not been pursued due to 1. the owner's hearing problem, and 2. the owner's most probable rejection of the idea that fixing the problem was at her expense, since our heat is in common and the perception is that any fault with it is the expense of the association. In other words, the ordinary human problems. Who will pay problems.

But perhaps not any of that. When I went upstairs to tell her these developments and that I would call the furnace company on Monday if she could get through the weekend (furnace companies and cardiac surgeons have in common that neither prefer to work on the weekends!), she shared that her heat had gone completely off. And it had. The baseboards were cold! So I checked her thermostat and saw that my previous setting of 77 degrees was gone. That was curious! So I set it again that high, and sat down while we grieved together about the whole thing, when suddenly -- she felt the baseboard in wonder--the heat had come back on!

It's pretty clearly a thermostat thing--even though I had discounted that because it had already been changed out twice. But so what. I googled the model unit she has and it has a ton of problems, erratic behavior being one of them. Really El Cheapo.

So I think possibly we're okay. We'll either learn how to control the beast, or get a better one. At least that's what she and I are hoping, she because she's 84 and poor, me because I'm 71 and tired and out of my league altogether, but it was this or live under a petty tyrant.

You are so kind to respond to the need of a stranger. May God reward you. I am so appreciative.

Might this thermostat have a battery backup that needs to be replaced?

SR

Thank you, I'm glad you thought of this. But mercifully I did too. The unit has a display, from the manual, that says Battery Low, and it isn't displayed. But this thermostat does not have good reviews, so even that display may not work.

I just meant to feel the temperature of the pipes with you hands the way you did before. I think that we are all impressed with your native troubleshooting skills, janetbaker76. I am glad that it is back working again.

It sounds like replacing the battery might be an inexpensive way to try to fix it.

Maybe if the electronic thermostat is going to be a continuing problem, an old-fashioned bimetal coil model should be installed:

http://www.ebay.com/itm/Honeywell-CT30A1005-Standard-Manual-Economy-Thermostat-New-Free-Shipping-/271807673264?hash=item3f48fff3b0:g:Q6cAAOSweW5VBkuC

I really don't like this one very much. I feel that it is too difficult for an older person to see. The scale is too small.