Heil HVAC Services in The Bay Area | Airstars

Heil furnaces and air conditioners communicate their internal status through a series of LED flashes on the control board. Knowing these codes can help you understand whether your system needs a simple maintenance task or a professional intervention.

Code 1 Flash: This indicates a system lockout, which usually occurs after three failed ignition attempts and often points to a problem with the gas valve or the flame sensor.

Code 2 Flashes: This represents a pressure switch stuck closed, meaning the system has detected a fault in the draft induction process before the cycle even began.

Code 3 Flashes: This is one of the most common codes we see, signaling a pressure switch stuck open, typically caused by a blocked flue or a failing inducer motor.

Code 4 Flashes: This indicates an open high-limit switch, which is a safety shutdown triggered when the furnace is overheating, usually due to a restricted air filter.

Code 5 Flashes: This signals a sensed flame with the gas valve de-energized, a serious technical error that requires an immediate professional safety check of the gas components.

Code 7 Flashes: This represents a twin fault or a communication error between two furnaces if you have a “twinned” setup, but it can also indicate a general control board failure.

For more technical background on the safety standards and performance ratings of these units, you can visit the Energy Star HVAC resource center.