Thermostat shows E4 and floor temperature reading is incorrect or dashes (floor heating models)

Safety: Turn off the breaker feeding the floor heating circuit and thermostat before working on wiring.

Steps to troubleshoot E4 (floor sensor short):

• 1. Inspect thermostat terminals: Remove the thermostat from the wall and inspect the floor sensor terminals. Ensure the two sensor wires are not touching each other outside the terminals and that no stray strands are bridging to adjacent terminals.
• 2. Disconnect sensor wires: Loosen the terminal screws and remove the two sensor wires from the thermostat.
• 3. Measure resistance: With a multimeter set to ohms, measure across the two sensor wires. A reading near 0 ohms indicates a short. Compare to the expected resistance from the Stelpro floor sensor datasheet.
• 4. Isolate cable sections (if possible): If there is a junction box between the thermostat and the floor probe, open it (power off) and measure resistance on each segment to locate where the short is occurring.
• 5. Inspect for mechanical damage: Consider recent work: new flooring, baseboard installation, or fasteners may have pierced the sensor cable. Look along accessible runs for staples or screws through the cable.
• 6. Replace sensor: If the probe or cable is shorted and cannot be repaired, replace the floor sensor with a Stelpro-compatible sensor. Use the existing conduit if one was installed. If no conduit was used and the cable is embedded in the floor, floor repair may be required.
• 7. Temporary workaround: If allowed by your application and thermostat model, configure the thermostat to use air temperature only until the sensor can be replaced. Be aware this may not protect floor coverings that require a maximum floor temperature.

Note: Persistent E4 after sensor replacement may indicate a fault on the thermostat main board; in that case, replace the thermostat.