Tech Tips: Troubleshooting a GFI Issue

Troubleshooting a Radiant Heat System GFI Issue


When you’ve installed a thermostat for a heated flooring system, if you see “GFI” displayed on the screen, that means that there may be a ground fault in the system. If you have a GFCI breaker that could be the cause, and it could also be because there is resistance between the wire and the ground. Testing for a ground fault is done by using a digital ohmmeter to see where ohms are coming from, and if there is any read from the black wire to the ground or from the red or yellow wire to the ground, you’ll need to fix the issue. In this video, you’ll learn how to test for and troubleshoot a GFI issue.

Video Transcript

If your thermostat displays GFI on the screen, it's telling you that it think its sees a ground fault. That ground fault sometimes is in the wire that's coming up from the roll or the system in your floor. Sometimes it's because you have a GFCI protected circuit breaker in your circuit breaker box. One important thing to remember is if you have a GFI circuit breaker in your box and you have a GFI controller in your thermostat, those two could fight one another. The idea is our thermostats have GFIs built into them so you do not need a GFCI protected breaker.

If you have a GFI problem, give us a call and we can send you this sheet. This is the ohms reading guide. This will tell you how to do the test on the cable. Today we're just going to talk real quickly on how to do it in real life. To do this all you're going to need is a digital ohmmeter. On this digital ohmmeter, we want to see if we're getting ohms across these two resistance wires and if we're getting resistance between the resistant wire and the ground or the other resistance wire and the ground.

The simple test is put the probes on the yellow and black. This is yellow and black because this system is 120. If this were 240 it would be red and black. We should be getting ohms here. We should not be getting ohms from the yellow or red wire to ground. You want to see if your ohmmeter giving you any ohms readings. It should be displaying OF or a one or INF. You should not be getting any ohms numbers across this. The same with the black to ground. These numbers should be INF, OFF or just a 1 displaying.

To recap, you don't want any reading from the black wire to ground or from the yellow or red wire to ground. That's how you troubleshoot a GFI issue with the WarmlyYours system.

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