Thermostat shows E3 and will not control floor heating properly (for models with floor sensor option)

Safety: Turn off power to the thermostat at the breaker before opening the wall box or touching any wiring.

Steps to troubleshoot E3 (floor sensor open):

• 1. Confirm model and mode: Verify that your Stelpro smart thermostat is configured to use a floor sensor (refer to the user manual). If no floor sensor is installed, change the configuration to 'air only' if supported.
• 2. Remove thermostat cover: Pull the thermostat off the wall plate and locate the floor sensor terminals (often labeled 'S1' and 'S2' or 'SENSOR').
• 3. Check sensor connections: Ensure the two floor sensor wires are firmly clamped under the terminal screws. Tighten gently if loose. Make sure no copper is exposed that could short to other terminals.
• 4. Inspect cable: Gently pull a small length of the sensor cable from the wall to check for nicks, cuts, or crushed insulation. If the cable was damaged during tile or floor installation, the sensor may be open.
• 5. Measure sensor resistance: Disconnect the two sensor wires from the thermostat. Use a multimeter set to ohms and measure across the two wires. A typical Stelpro floor sensor will read several kΩ at room temperature. If the reading is infinite (open), the sensor or cable is broken.
• 6. Check at floor end (if accessible): If the sensor junction box or probe end is accessible, measure resistance directly at the probe. If it reads correctly there but not at the thermostat, the cable between is damaged.
• 7. Replace floor sensor: If the sensor is open, it must be replaced with a compatible Stelpro floor sensor. This may require removing floor covering if the sensor was embedded in mortar. In some installations, a spare sensor was installed in a second conduit—check for this before opening the floor.
• 8. Reconfigure thermostat: If you cannot replace the sensor immediately, and your application allows, configure the thermostat to use air temperature only (if supported) as a temporary workaround.

Warning: Do not energize floor heating circuits with a known faulty sensor in 'floor control' mode; overheating and floor damage may occur.