If your thermostat hasn’t been produced since 1998 or before, all the supplies on the shelves may have been depleted. One option I have suggested is that if you just must replace it with a Chronotherm III, and the only one left that will do the job is the T8601C1021 or some other one similar, it may require an additional wire that the old one did not need. You may have an extra one in the bundle of wires that come from the wall. You connect it to the C terminal on the thermostat and then in the furnace connect the other end of it to the C terminal there. This is a wire that connects the other side of the transformer voltage to the thermostat. It won’t work without it.

If you don’t have a spare wire, then you have to run one to the thermostat and heater. Maybe this would be easy or maybe it would be nearly impossible. You decide.

However, if you don’t mind new technology and you want the current production (and better) model and don’t want the hassle of trying to run an extra wire, then you need to look at the Honeywell® VisionPro™ which is the replacement for obsolete Chronotherm III or IV thermostats.

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Honeywell® VisionPro
Replacement for obsolete Chronotherm III/IV

You can do it yourself. Your old thermostat may have terminals W,G,R,Rc and Y. The new VisionPRO™ has terminals that match that exactly. If you have the Chronotherm III, just remove the two screws on the front of the thermostat. You can then lift off the front part of it. While you have the front part off the wall, make a note of the wires that come out of the wall and to which terminals they attach. Ignore the terminals that do not have wires attached that come through the wall.

You just unplug your heater or turn off the 240 Vac or 125 Vac to the heater and the electricity to the thermostat will be “dead”. Remove the old thermostat and the subbase off the wall and set it aside.

Mount the new subbase and attach the W,G,R,Rc and Y, etc. to the same terminals. One thing to look for, if your old thermostat had a jumper wire between the R and Rc terminal, then you leave the jumper (factory installed) in place on the new thermostat. If there was no jumper on the old thermostat between R and Rc, then you remove the jumper that is in place on the new thermostat also.

The new thermostat will operate on battery power alone if you do not have the C terminal connected to a wire. Hundreds of thousands of them (including mine) are doing it very successfully already. It is not a problem.

You will, however, need to do something new. You must set the “Installation Options” in an “installer options menu” in the new VisionPRO™ thermostat. It is not difficult and if while you are doing it you have questions, then you can always call me and I will walk you through it. I don’t mind. I am central time and am available from 8:00 AM until about 10:00 PM daily. If you chose to buy that discount store model at their lower price then you should call them for tech support, not me.

All the information is shown in a booklet that comes with the new thermostat. It even shows pictures of where to place your finger on the thermostat. All you have to do is follow instructions and if you falter, call me.

One marvelous new thing about the new thermostat is that you can set it so it will show not only Heat, OFF, Cool, but it can be set to show Heat, Off, Cool and Automatic changeover from HEAT to COOLING and vice versa. This is wonderful. The only problem you will have because of it is that you now will never know what the temperature is outdoors. Your home will perpetually be comfortable.

Here are some of the features of the new VisionPRO thermostat that you might want to set:

*  You will set the options to the correct year, month, day and time.

*  Then choose 1 heat/ 1 cool (it is already factory default set to this one).

*  You can set the temperature limits on the heating and cooling. You could set it, for example, so that no one could accidentally set the heat to 90° F and leave it. You could also set the cooling to 68° F (or something else) so that no one could set it below 68° F.

*  You can even set it so that no one but you has access to the settings. You could allow others to only have access to Temporary Temperature changes, but not to the program settings.

*  You can select individual 7 day programs. You can even choose to allow all four program periods as you had before or reduce it to just two per day. It uses Wake, Leave, Return and Sleep just as you had before on the Chronotherm III.

*  You can set an option to remind you when to change or clean your filter, UV light, or when humidifier pad replacement is needed.

You don’t have to set any of the things above if you don’t want to. I would suggest you do set the calendar and time and set the system to have automatic changeover.

The automatic changeover from heat to cool or vice versa is so good. You will find that you never know what the temperature is outside because your house is perpetually comfortable regardless of conditions outside. You never wake up to a cold floor again.

Options available for the new VisionPRO:

*  Remote room temperature sensors. You can have up to 12 of them—one in each room. It will average all of the temperatures and run the system accordingly.

*  Remote outdoor temperature. This will allow the outdoor temperature to be displayed right on the face of the thermostat at all times.

* NOTE: Both of the two options above require wires to be run to each device.