Thermostat shows E10 and the screen may be dim or unresponsive

Safety: Turn off the breaker before opening the thermostat. Use a voltage tester to confirm power is off.

Steps to troubleshoot E10 (low voltage):

• 1. Confirm circuit type: Verify whether your Stelpro smart thermostat is designed for line-voltage (120/240 V) or low-voltage (24 V) systems and ensure it is installed on the correct type of circuit.
• 2. Check wiring diagram: Compare the actual wiring in the wall box to the Stelpro installation diagram. Ensure line (L), load, neutral (if required), and ground are correctly connected.
• 3. Tighten terminals: With power OFF, tighten all terminal screws on the thermostat and in the wall box wire connectors. Loose connections can cause intermittent low voltage.
• 4. Measure supply voltage: Turn power ON and carefully measure voltage between line and neutral (or line and line for 240 V) at the thermostat terminals using a multimeter. It should match the circuit rating within ±10%. If it is significantly low, the issue is in the house wiring or breaker.
• 5. Inspect breaker and connections: Turn power OFF and inspect the breaker and panel connections for corrosion or looseness. This work is best done by a licensed electrician.
• 6. Replace thermostat: If supply voltage is correct but E10 persists, the internal power supply circuit on the thermostat board may be defective. Replace the thermostat.

Warning: Working inside an electrical panel is hazardous. If you are not trained, hire a licensed electrician.