I just did a mad-dash cleaning around the apartment. I noticed that the heater in the apartment was not turning on. I checked it out, and the thermostat was blank, no digital display showing the temperature. I thought perhaps the maintenance man would have to come.
I called the super after I had finished cleaning, and he told me that usually means the batteries are dead, and to just replace them, if I had them. The face of the unit pulls off easily.
Thankfully, I had batteries in the apartment, and now it's working again, and as a side bonus, the apartment is clean.