Furnace shuts down shortly after ignition; display indicates overheat or high limit trip

Safety: Turn off power before removing panels. Components may be hot.

• Check air filter: Locate the return air filter in the furnace or return grille. If it is dirty or collapsed, replace it with the correct size and airflow rating recommended by IVT.
• Inspect supply and return vents: Ensure that supply registers and return grilles throughout the home are open and not blocked by furniture, rugs, or closed dampers.
• Verify circulation fan operation: With panels in place, restore power and set the thermostat fan to "ON". If the IVT circulation blower does not run, the blower motor, capacitor, or control board fan relay may be faulty.
• Check high limit switch: After power is off and the unit has cooled, locate the high limit thermostat mounted on the heat exchanger panel. Inspect wiring and ensure it is firmly attached to the metal surface. Some IVT models use manual-reset limits; press the reset button if present.

If the furnace repeatedly overheats after these checks, have a technician inspect the heat exchanger, blower speed settings, and ductwork sizing.