Our Honeywell programmable thermostat is close to 20 years old. Within the past week or so I have notice that while the program shows the heat should be at 68 degrees, the thermostat is reading as low as 64 degrees and not furnace does not kick in. Eventually the furnace kicks in, but it is not maintaining a steady temperature. Our furnace was replaced in 2002 and was serviced last winter. Is it possible the thermostat needs to be replaced?

Good Morning, and yes you said it. Anytime a stat doesn't come on when it is set for a call for heat or cooling, the sensor on the subbase of the stat has lost its ability to sense the correct temperature. I have seen mechanical stats last as long as 25 plus years, but that's truly amazing for a digital stat to last that long. Yes, replace the thermostat. I don't know what kind of system you have, but if its a gas furnace with an a/c, the wiring will look like this. You will have terminals marked R, Red, for the 24 volt hot wire, G, Green, Y, Yellow, and W, White for heat. Going back to the red wire, it should have RC and RH on it. There will be a normally red wire connecting the 2 terminals.The Red wire coming in can connect to either one, as they are all together. The new stat will come with the new Red jumper wire attached. So, if you do have a gas heater, this is very easy to install. The only terminals you will need to use are RH to RC for the incoming red, Y, G, and W for heat. Y is for cool, and G is for fan. Very easy. Now if you have a heat-pump, they have many more terminals and can be a problem wiring them. If you have gas, forget the heat pump. I wont confuse you by going there. If it is a heat-pump, contact me in the comment box to let me know, and I can help you there also. Get a new stat at Home Depot, Lowe's Hardware, or O.S. Hardware. You want a 5 day, 2 day programmable Heating and cooling thermostat, 24 volts.It will have everything you need. See if it takes batteries for the display, they may not come with those, it will say on the box. Turn off your power to heater, so you won't short out the new one.They come in 2 sections, first the stat that just snaps on, and the subbase that is screwed to the wall. It will have the wiring terminals on it. Remove a couple of screws and loosen wires and remove. Be sure you write down how the wires go in case they used different colors, you never know. You will be all set. Store the manual in a safe place for future use. I wish you the best.
Shastalaker7
A/C, Heating, & Refrigeration Contractor.
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