Hi Deborahdpollard,
Nobody likes error codes, so let me demystify things for you! The E74 error code means no power to the Rh wire is being detected. Here's some things you can check.
1. Check the system power
First, make sure the power to your system is on. The power switch will usually be in your breaker box or fuse box, but in some homes it will look like a light switch near the heating or cooling equipment.
- There may be a single switch, or two switches: one for heating and one for cooling. Make sure the power is on for both then check your thermostat.
- After you check the power, go to your thermostat and check if it’s working.
2. Check the thermostat wires
Important: Protect yourself and your thermostat and your system. Turn off power to your system and thermostat at the breaker or fuse box before exposing or adjusting any wiring.
- Pull off the thermostat display.
- Check that each wire is fully inserted into its connector and that every connector with a wire is down.
- Check that each wire has ⅜ inch (6mm) of exposed wire.
- Turn the power to your system back on and check to see if your thermostat is working.
- Check that each wire is connected properly to the system board.
If you’ve completed the troubleshooting steps above and your thermostat still isn’t working correctly, I'd recommend contacting a local pro for more help.
