Electric radiant heating troubleshoot help!

Hi all,

I've recently installed and tiled over a 10sq ft electric heating mat in a bathroom. The bathroom has a 120v circuit with a GFI outlet which powers the thermostat for this heating mat (and an overhead lamp). I've checked the continuity on the mat before, during and after installation and it's been the same: 119 ohms (120ohms expected per label), and 1 (infinity) on the ground and black/white.

The thermostat powers on ok (Honeywell TH115-120S), and there's a call for heat. The temp sensor wire checked out ok too. There appears to be no issues, but after over 1 hour, the mat does not heat up (the temperature on the sensor did not change of course). Upon inspection of the wiring, when everything is connected, the thermostat Load wire does not send power to the mat. If I disconnect the mat wire, the Load wire from the thermostat DOES have power (checked with a V meter).

There are no GFI breaks in the circuit and the continuity checks out ok. I'm not sure if this a thermostat problem or if there's something I'm missing here. Help!

Thanks!

 

It appears to be a thermostat issue.

You can remove the stat and directly connect the radiant for an hour but from your measurements I'm sure you''ll get heat.

I know there are four wires.... two white and two black. Are they labeled LINE and LOAD ?
Line is incoming power and load is the radiant.

If it is connected correctly.... the stat would appear to be defective.

 

Ok thanks, I actually went ahead and bypassed the tstat and the floors did get warm in under an hour. They are installed over concrete slab so i don't expect a hot floor, but the heat difference was considerable compared to where the mat is not there. I did triple check the wiring on the tstat so I'm confident that can't be the issue. Will get the tstat replaced ASAP. Thanks!

 

The floor just needs to be warm. Hot to the touch could induce cracking.
Let us know if the new stat corrects the problem.