Thermostat display shows E1 and heating does not turn on

Safety first: Turn off power to the thermostat at the breaker panel before removing it from the wall. Verify power is off with a non-contact voltage tester.

Steps to troubleshoot E1 (sensor open):

• 1. Power cycle: Turn the breaker OFF for 2 minutes, then ON. If E1 clears temporarily and returns, continue with hardware checks.
• 2. Remove thermostat from wall plate: Gently pull the Stelpro smart thermostat straight out from the wall base. Inspect the rear pins and wall plate contacts for bent or damaged pins.
• 3. Inspect internal sensor area: On many Stelpro smart thermostats, the room sensor is an NTC thermistor on the main PCB near the air vents. Look for broken or cracked components, or signs of overheating.
• 4. Check wiring connections: Ensure the line (L), load (L1/L2), and neutral (if used) are firmly secured in the thermostat terminal block. A loose neutral or common can cause false sensor errors.
• 5. Measure sensor resistance (advanced): With power OFF and thermostat removed, access the NTC sensor leads on the PCB (refer to Stelpro service documentation). Use a multimeter set to ohms. At room temperature (~20–25°C), the NTC should show a stable resistance (commonly 10kΩ or similar). If the reading is infinite (open), the sensor is defective.
• 6. Clean connectors: If the thermostat uses a plug-in harness for the sensor, disconnect and reconnect it several times to clean oxidation. Inspect for broken wires in the harness.
• 7. Replace thermostat if sensor is open: The internal sensor on Stelpro smart thermostats is typically not field-replaceable. If the NTC is open or physically damaged, replace the entire thermostat assembly with a compatible Stelpro smart model.

When to call a technician: If you are not comfortable opening the thermostat or measuring resistance on the PCB, or if the unit is under warranty, contact a qualified electrician or Stelpro-authorized technician.