Setting the date on a Honeywell RTH7400 Thermostat

My Honewell RTH7400 somehow time-travelled a day into the future, and it turns out you have to “hack” it to fix the date on a hidden diagnostic menu. Full credit to Daniel from for the solution. RTH7400

  1. Select System
  2. Press and Hold Fan
  3. Should see 0120 with setting 20 blinking
  4. Press next to 0130, this is the year
  5. Press next to 0140, this is the month
  6. Press next to 0150, this is the day
  7. Press Done.

I’ve also grabbed the PDF instruction manual for the RTH7000-series in case you find it handy!