If you get a sensor fault message on the Home Page of your RF500 System Gateway, then you should check the condition of the Transmitter referenced and importantly its probe and connection. If possible, we suggest that you swap the probe for another known good working one, in order to eliminate the probe as the source of the problem.
If the Transmitter in question just has an integral sensor (RF513) or the connected probes have all been tested on other devices and found to be working OK, then you will need to contact us, as your Transmitter could be faulty.