LED flashes code 42; inducer or outdoor unit may not respond correctly, furnace may short-cycle.

Safety: Turn off power before working on control wiring or motors.

• Step 1 – Check thermostat wiring: Verify that the thermostat is wired correctly to R, W, Y, G, and C per the Tempstar wiring diagram. Correct any miswiring.
• Step 2 – Inspect Y circuit: Disconnect the Y wire at the furnace and see if the code clears. If so, inspect the cable to the outdoor unit for shorts or damage.
• Step 3 – Test inducer motor: During a call for heat, check for 120V at the inducer motor leads. If voltage is present but the motor does not run, replace the Tempstar inducer assembly.
• Step 4 – Inspect control board: If the inducer never receives power, the inducer relay on the control board may be faulty. Look for burn marks or heat damage. Replace the control board if necessary.