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Phil, Mechanical Engineer
Category: HVAC
Satisfied Customers: 8425
Experience:  Retired HVAC/ Electrical & Boiler contractor. Industrial
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I just purchased a new Honeywell Smart Thermostat and wanted

Customer Question

Good morning, I just purchased a new Honeywell Smart Thermostat and wanted to replace our old thermostat. I followed the instructions and turned off the AC (as instructed) from our circut breaker box. However when I turned the breaker back on nothing happened. The thermostat is blank and now I do not have power to our Lennox Merit Series furnace.
I then I looked at the #3 fuse and it was fried. I replaced with a new fuse and turned the unit back on, but nothing has worked. Any suggestions.
Submitted: 1 year ago.
Category: HVAC
Expert:  Phil replied 1 year ago.

Hello, there was a error made in wiring the thermostat. These are not always as easy to wire as the promotional material and even the wiring instructions indicate.

If you can give me the model number of the new Honeywell smart thermostat, and a photo of the printed circuit card inside your furnace, where the thermostat wires attach that will help, we can begin there.

Tell me if you have a heat pump sitting outside or not, and if it only runs in warm weather or if it runs in the winter a lot as well.

Use the paper clip icon at top right of the tool bar to attach photo's

We can go from there.

Customer: replied 1 year ago.
The model Number of the Thermostat is RTH9580 Wifi. The heating unit is inside the house (Basement). I'll be sending the pictures shortly.
Customer: replied 1 year ago.
Attached is a photo
Customer: replied 1 year ago.
Also just to let you know I put my old unit back on thinking there was defect with the new thermostat and when I did, it also came back as a blank screen. I had 5 wires (Blue, Green, White, Red & Yellow) and matched according to the specifications.
Expert:  Phil replied 1 year ago.
Thanks for the picture.
I need another one however.
copy paste that to your browser.
If you have air conditioning, you will also have a unit that sits outside, you can follow the two copper tubes attached to the cooling coil to it outside. The photo you sent is of the furnace in the basement only.
Let me know what you can find, we can go from there.