Bryant 340MAV Error Code Continuous ON: Normal Operation
What Does Code Continuous ON Mean?
When the diagnostic LED on the Bryant 340MAV control board glows continuously without flashing, the furnace is in normal standby mode. The Carrier integrated furnace control has 24VAC power and is operating correctly, but no call for heat is active from the thermostat — the R-W contacts are open.
This status appears between heating cycles after a call for heat ends and the circulating blower shuts down, or any time the thermostat is satisfied. If the furnace is part of a system with central air conditioning, the continuous LED may also appear during cooling or fan-only operation, since those modes operate independently of the gas heating circuit.
The 340MAV uses a 2-digit LED blink code system where the first digit is the number of short flashes and the second is the number of long flashes. A continuously illuminated LED is distinct from all blink codes and simply indicates a powered, idle state — the healthy counterpart to a continuously off LED (code-off), which means the board has lost power entirely.
What You'll Notice
- The control board's diagnostic LED glows steadily, with no short or long flash pattern
- The furnace is quiet and idle between heating cycles, with no error code flashing
How This Is Diagnosed
A steady LED is confirmed simply by reading the diagnostic light through the access panel or sight glass and noting there is no short/long flash pattern — it is continuously on. A technician treats this as the normal powered, idle state. If heat is expected but not delivered, the check moves to the thermostat call (R-W) and the 24VAC supply rather than the control board, since a solid LED already shows the board itself is healthy.
- The furnace does not start heating when the thermostat is set to Heat and raised above room temperature
- The LED is solid but you suspect the thermostat or its wiring is not sending a heat call
Frequently Asked Questions
My Bryant 340MAV LED is solid on but the house is cold — is the board broken?
A solid LED means the board is powered and healthy; it does not mean a heat call is active. Check that the thermostat is set to Heat and above room temperature, and that its batteries are good.
Is a steady light on the furnace control board bad?
No. On the 340MAV a continuous (non-flashing) LED is the normal standby indication that the board has 24VAC power and no stored fault.
✓ Verified against manufacturer service manual — March 2026