Actually, from what I've gathered so far, downstairs is far more likely to call for / genuinely need Aux heat. It is possible, perhaps even likely, that absent very careful sizing of ducts and dampers, upstairs 'steals' more heat than needed, starving downstairs already hobbled by size, glass, elevation. (Then again, considerations of cooling upstairs may dictate larger than minimum necessary ductwork for heating upstairs - always tradeoffs)

This is all hobbled by the innate shortcomings of assisting by internet

BTW Geofan - FYI you can 'edit' an earlier post rather than posting again...

I'll bear in mind the tip about Ranco controls

This would be my assessment as well.

Connie / Engineer:
johncomyn's tstat, posted in another thread does number 4. It is Climatemaster non-programmmable ATA32U01. It operates aux heat from 1 to 4 degrees, selectable, below setpoint. It also delays the start of aux heat from 0 to 120 minutes, selectable, from the moment the actual temp matches the set differential, e.g. it can be set, easily, to start electric heat after 2 hours from the time the actual room temp falls to 66 degrees, given a setpoint of 70 degrees. I don't know the cost of this tstat. I have one similar, but programmable with humidity sensor, costing perhaps around $200. They accept a remote sensor, if needed.
Connie, could you be more specific than TH 5000 series, and post the actual model of your tstat? Could it be a Honeywell labeled as Geocomfort? It may already be capable of doing this.
Regards, Masoud

Thanks again for feeding this topic. So I browse the manual again. Masoud, yes I believe it is manufactured by Honeywell and only labeled as Geocomfort as I found it at the last page. Now this manual says covers the following models:

TH5100D : for Heat only systems
TH5110D : for 1 Heat/ 1 Cool Systems
TH5220D : For up to 2 Heat/ 2 Cool Systems
TH5320U: For up to 3 Heat/2 Cool Systems

I hope this will help. I can open the battery holder to see the actual model but I'm worried that I might screw up the settings.

Connie / Engineer:
Honeywell TH5220 seems to be the thermostat installed. This tstat has two installer set options for aux heat control. 1- Comfort and 2- Economy. Comfort is the default setting. It activates aux heat as soon as the room temp falls "a few" factory-set degrees below the setpoint. Economy setting allows the thermostat to wait "a preset time" period, also factory-set, before the aux heat is activated. This option gives compressor some time for attempting to bring temp up to the setpoint. So, it is a time delay option for aux heat. The manufacturer recommends these options to be set by the installer. I saw this info and and instructions on how to change options on the web, at:
thermostatshop.com/manuals/Th52220%20Installation.pdf.
Regards, Masoud

I don't believe you'll lose settings by removing batteries for a few minutes. Manual should confirm that.

I have Honeywell 8xxx (don't remember which) and install manual shows all parameters and how to set them. It isn't hard but takes attention to detail and knowledge. A reasonable precaution might be to walk through all menu settings and note their 'as found' settings before tinkering.