Before returning the gauge, I would check that my wiring is correct. With a J/K type thermocouple they only put out a mV signal and are +/- sensitive. You can even download off the web a J/K vs mV chart to correlate back to what you should be seeing on the 2 wires off the probe. You will need a DVM (Digital Volt Meter than reads mV) to do this. As well any improper connections will drop or impede the mV from registering properly on the gauge. A thermocouple is made up of 2 dis-similar metals that are welded together at the tip, which when connected will produce a mV output. Usually when they fail they fail high or Low, not usually in between.