Why are my floor heating system resistance readings not the same after several years?
It is very uncommon for a mat to fail over time. Because there are no moving parts and no leaking or freezing liquids, systems will last a very long time. However, if repairs are done to the floor, fixed furniture or any related area in the room, damage can be done to the cable and needs to be addressed. Common instances are trim work, tile repair, grout cleaning, and door stops.
It is not impossible that a slight cable damage was not spotted during the installation and reveals itself as a break or ground leak after a few weeks or months of operation. Again, this is uncommon, but possible. Contact Warmup to rent a TDR meter and help locate the spot of the issue under the floor.