Customer states none of the thermostats function. Arrived and found zone control board powered and calling for heat. All dampers are operating properly with full range of motion. Found four year-old gas, furnace, indicating a flash code “open low voltage circuit”. Traced low voltage circuit and found 2 areas of rub out at the limit wires against the inducer housing. Repaired insulation on wire, replaced 3 amp fuse. Check cycled and tested all heating operations. Checked manifold gas pressure. Tested overflow, safety switches and found a broken pan safety switch unable to test. Recommend replacing pan safety switch. All operations are ok otherwise. Additional estimate was left to install two isolation valves on the existing gas manifold. Thank you for trusting Dawsons with your heating and air needs.