Cold Loop checking: Checking of wires continuity of respective field instrument-Junction box-DCS/PLC marshalling panel terminal. Hot loop checking: Once you power up your field instrument through DCS/PLC system, by stimulating process input from respective field instrument and cross check its response at DCS/PLC sytsem. There is no such differnce as a cold and hot loop check. There is a wiring/ point to point that all should do before carrying out a loop check from field device to DCS display.