Hi there
I would like some advice around the use of an infloor heating system's thermostat (Easy heat). 2 years ago we installed an infloor heating system with a sensor wire into the mortar underneath the tiles. The thermostat is a 7 day programmable one. To this day we have not done anything to the tiles that could have damaged the sensor wiring (such as drilling etc)

For the first year the thermostat and the floor worked fine. Great heat on your feet. However, we turned it off for the summer months and when we turned it back on the reading on the thermostat that indicates actual floor heat went up to 120F even through the tiles are stone cold and no heat can be felt. There is no heater or anything near the sensor causing it to perhaps to read that temperature instead and making the thermostat go to the maximum level the floor can be set to. Because that is the maximum level, the heating systeme won't come on.
Thinking perhaps the thermostat was defective we removed it and re-installed it thinking it would reset itself. No luck. So we replaced it with a new thermostat. This has not fixed the problem and the same is happening. At least it ruled out tha thermostat as a cause. We were able to get the floor to warm up, although the temperature was appr 86 or so, the thermostat required to be set higher in order for the heat to go up to a nice temperature. It seems to be that for some reason the thermostat receives a "message" that the floor is at the maximum hear even though that is not the case. So it is back up at 120 and no heat coming on as a result of that.
Does anyone have any idea what might be going on? The sensor has not been touched or the floor drilled in or anything. The fact that the heat did come on for a while tells me it all is working but somehow the temparture readings are not correct. All the components are easy heat. We called them but did not receive any call back after several attempts, let alone advice on what the issue could be.