Only one floor sensor should be connected to the thermostat. The second one, when present, is fixed to the floor but not connected to the thermostat; this precaution avoids having to break the floor covering in case the sensor is compromised.
If a sensor needs to be replaced, it can be inserted in the grout line between two tiles, simplifying the work.
If this is not possible, the best thing to do is to locate the heating cable using an infrared camera before removing the floor covering. Those cameras are now affordable and are available at tool rental centers.
The new sensor must be installed between 2 cable runs, at least 1 foot in the heated area, far from any source of heat or cold and without crossing the heating cable.
Be careful not to damage the heating cable when removing the floor covering. Scrape the mortar between 2 cable runs, allowing you to route the sensor’s wire to the wall and then to the thermostat’s connection box.
Before installing the sensor, remove any excess mortar to easily replace the floor covering.
Set the sensor and its wire to the floor using a hot glue gun. Note that the temperature sensor is located at the end of the wire and must be installed exactly halfway between 2 runs of heating cable.
When installing your new floor covering, make sure that the heating cable and the sensor are completely embedded in mortar.
If you are not comfortable doing this yourself, contact a heating cable repairer or True Comfort Customer Service.