Electric heat tapes prevent water pipes from freezing. The tapes are constructed from two insulated wires that emit heat when electrical energy is supplied to the circuit. Modern heat tapes generally have an in-line thermostat installed to control the operation. The thermostat is factory set to turn on the electrical power when temperatures reach 40 degrees F or below. Testing the heat tape for operation is a two-fold process. Both tests require no tools.
Shut off all electrical power to the heat tape. This may entail switching off the circuit breaker or pulling the fuse that supplies power to the electrical circuit. It may also entail unplugging the heat cord end from the wall outlet.
Remove all insulation that may be covering the heat tape. You must have full visual access to the installed heat tape application.
Run your hand over the surface of the heat tape. Inspect the insulation for any cracks, nicks or breaks. If the electrical wire insulation has any surface defect, stop the test. Remove the defective heat tape and install a new heat tape as per the manufacturers instructions.
Fill the plastic food grade bag with ice. Secure the top of the bag so it will close. Locate the in-line thermostat on the heat tape. The thermostat will be near the plug-in end of the heat tape, and mounted to the water pipe.
Lay the plastic bag of ice over the heat tape thermostat. Allow it to set for 30 minutes. This amount of time will be sufficient to drop the temperature of the thermostat below 40 degrees F. If possible, do not allow water to flow through the water pipe you are testing.
Switch the power source back on to the heat tape. Feel along the length of the heat tape. It should be getting warm. If the heat tape fails to warm up, after 10 minutes, the thermostat or the heat tape itself is bad. Remove the heat tape and install a new unit.