Thermostate backup batteries continuously die

I’ve had this old Honeywell thermostat for quite possibly 20 years. It’s a 7 day programmable thermostat with a battery backup (2 AAs). A couple months ago I had someone come out to look at my AC. He was not my normal guy, because I have a home warranty and thought it would be a good idea to use them. Ever since his visit, the batteries only last about a week. Before his visit, I couldn’t tell you how long they lasted. The thermostat has 4 wires, Green connected to the G screw, Yellow connected to the Y, White connected to the W and Red connected to the R (there’s a jumper connecting that to the RC. FYI, the thermostat model is Honeywell rth7400/7500. All the wires seem secure at both ends. I just had my regular guy come out and do a fall check on the heater and he says everything is fine, that it has to be the thermostat needs to be replaced. It is old but seems like it’s way too much of a coincidence that this started when the home warranty guys were poking around. Do you guys concur with him that the thermostat just started eating through batteries like there’s no tomorrow? Or is it more likely that something in the HVAC unit isn’t connected and supplying power to the thermostat, making it use batteries instead of A/C power? Also, is it possible if the thermostat is set to either heat or AC, it provides power but if the thermostat is set to off, it just uses the batteries (we’ve had more nice days this summer than any other I think and haven’t needed it on)?

Home warranty companies are a scam and worthless.

Find a real service provider!

With only 4 wires your thermostat is running off the batteries only vs the furnace transformer.

With that wiring, you are NOT using ac power, but the batteries, to keep the program, time and day. It has ALWAYS done that. It can steal power to do this and to operate, but batteries are needed.

I would call it a coincidence, that is old and the retail(R in the model number) version is not as feature packed and robust as the pro version of Honeywell’s line, thus the 1 year warranty vs 5 year.

Get it replaced with your usual guy’s recommendation and drop the warranty company. In the end, the warranty company will NOT make you whole when it comes to needing a repair or replacement. They are an insurance company and their job is to make money and to pay out as little as possible using all the fine print in the contract you agreed to but probably did not fully read or understand.

I had one do this. The thermostat has gone bad. Only Honeywell I’ve ever go bad on it’s own. Chewed through batteries in about 18 days.

Thank you everyone for your input. Time to get a new thermostat. My only concern was that if I replaced it and there was still something wrong outside of the thermostat. I now know that it isn’t. Thanks again.

When you get the new stat put fresh batts in the old one and check it in a week or 2.

I concur it was a coincidence.
I was at a customers home this week and while standing in the basement the light bulb died. I was waiting for the old “it worked fine until you were here”

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