This is a sensor problem, here are a few fixes:

1. Check to ensure the thermostat is firmly connected to the “C” and “D” ports behind the face plate of the thermostat.
2. If you did not install a floor sensor or it is damaged, set the thermostat to red ambient temperature:
   1. Press the OK button twice to bring up the main menu.
   2. Use the UP or DOWN buttons to scroll to SETTINGS, then press OK.
   3. Use the UP or DOWN buttons to scroll to APPLICATION, then press OK.
   4. Use the UP or DOWN buttons to select ROOM, then press OK.
   5. Set desired temperature (some model of thermostat)
   6. Use the UP or DOWN buttons to scroll to EXIT, then press OK. (do this twice)
   7. Your thermostat will now measure the temperature of the room and NOT the floor sensor. (TIP: You may have to adjust the thermostat temperature higher or lower than expected to achieve desired floor temperature.)
3. Test the floor sensor to measure resistance to check for resistance.
   1. Set your multimeter to the 200k Ohm (Ω) setting.
   2. touch a probe to each end of the sensor wire.
   3. A functioning floor sensor should get a reading between 9,000 and 25,000 ohms, if the sensor fails this test, please see #2 for how to switch to ambient air sensor.

NOTE: Whenever working on ANY wiring for the thermostat, please TURN OFF the breaker powering the thermostat and floor heating system.

The black connections points at the end of the heating cable and between the red heating cable and the black cold lead are engineered connection points and WILL heat up and it is crucial that BOTH of these connection points get fully embedded in thinset and/or mortar.

Since these connection points are thicker than the heating element, best advice is to chisel out a small groove for the connection point to sit in, in order to lower it’s profile.

DO NOT DAMAGE OR REMOVE EITHER OF THESE CONNECTION POINTS. THEY CANNOT BE REPAIRED.

The floor sensor is located inside the box containing the thermostat. It is a separate thin-gauge cable from the heating mat/cable.

The black cable that attaches to the red heating cable is called the COLD LEAD (as it does NOT heat up). It is designed to be able to be cut and or shortened in order to better accommodate reaching the Thermostat location.

There are a few things to do to mitigate excess cable/mat:

1. The best advice is if you still can return the mat/cable to Amazon especially if you have a large amount of excess cable and get the next size system down.
2. Tighten spacing between cable spacing (keep at least 2 inches of space between heating cable) and DO NOT overlap ANY heating cables or heating cable over any other cable.
3. Remove cable from the mat and run it into areas where the mat does not fit. (Use a small amount of tape or glue to keep the heating cable in place.)

Reminder, DO NOT, UNDER ANY CIRCUMSTANCES, CUT (OR ATTEMPT TO SHORTEN) THE READ HEATING CABLE. The heating cable is specifically engineered to be the length it is.