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35+ year old furnace was not heating. 2 year old Wifi thermostat was the problem.


After troubleshooting my furnace I realized that the problem wasn’t in my furnace. The problem was that my wifi thermostat was not responding to commands

I was working in my home office and noticed that the furnace wasn’t running. The forced hot air furnace is 35 plus years old and belongs in a museum, not a house, but I’ll get around to that later. I found that the problem wasn’t the furnace. I leave the settings as a set back during the day to 60 degrees. The thermostat is a Honeywell WiFi enabled thermostat. Since my son and I were home, I pushed the heat up using the phone app. Normally, I get an email from Honeywell if the attempted settings change didn’t take. After about 15 minutes, I realized that the heat still wasn’t on.  I tried setting it from the desktop app. It showed that I set the temperature for 66. This is a decent temperature when the woodstove is going.

After about 15 minutes more, the heater still didn’t go on. My first thought was that there was something wrong with the heater. After some research, I decided to replace the thermocouple. The local supply house had one. A half hour later, I was ready to try again. Still no heat.

I was really hoping to get through this winter with the existing furnace. The thought of trying to find a replacement gas valve seemed daunting. Perhaps the Smithsonian would have one.

I was going to grab a voltmeter to see if I was getting 24 volts to the valve. Then I decided to check the thermostat on the wall. The thermostat was set at 60 and there was no ‘heat on’ indicator. (The photo of the thermostat below is of normal operation).  I manually bumped up the temperature and the heater fired right up.

The problem was that the thermostat was not getting the change notice from the desktop or phone apps. Further, I was not getting a failure notice. I’m not sure if the issue was with the Honeywell site, which passes commands to the thermostat, or if there was a problem with my home WiFi.

I don’t feel too bad about replacing the thermocouple. They are supposed to last 3 or 4 years. This one has been installed for around 10 years.

Thermostat App
Honeywell wifi Thermostat App
Honeywell wifi Thermostat

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