Bryant 340MAV Error Code Continuous OFF: No Power
What Does Code Continuous OFF Mean?
When the LED on your Bryant 340MAV control board is continuously off, it means the board is not receiving electrical power. The furnace cannot operate at all in this state because the Carrier integrated furnace control manages every function from ignition to the blower motor.
The most common cause is a tripped circuit breaker or blown fuse at your home's electrical panel. The second most likely cause is the furnace power switch being turned off. This switch looks like a standard light switch and is usually located on or near the furnace — it can easily be bumped to the off position accidentally.
If both the breaker and power switch are fine, the problem may be a faulty transformer or wiring issue inside the furnace. The manual specifies checking for 115 VAC at L1 and L2, and 24 VAC at SEC-1 and SEC-2, but these measurements require specialized equipment and should be left to a qualified technician. A completely dark LED is distinct from code 24 (secondary voltage fuse open), where the 24VAC fuse has blown from a short — with code-off there is often no power reaching the board at all.
What You'll Notice
- The furnace is completely unresponsive — no heat, no blower, and no sounds even when the thermostat is calling for heat
- The diagnostic LED on the control board is completely dark, with no flashing and no steady light, when you look through the access panel
- The thermostat display may be blank if it draws its power from the furnace's 24VAC common wire
- The problem may have started right after a breaker tripped, a power flicker, or running another appliance on the same circuit
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Tripped circuit breaker or blown fuse | Most common | ✓ DIY fix → |
| Furnace power switch turned off | Common | ✓ DIY fix → |
| Faulty transformer or wiring | Uncommon | ✗ Call a pro → |
How to Fix It: Check the Circuit Breaker and Power Switch
What You'll Need
Steps
- Turn off power and gas supply as a precaution Before investigating, turn off the furnace switch and turn the gas shutoff valve near the furnace to the OFF position (perpendicular to the pipe). If you smell gas at any point, leave immediately and call your gas company.
- Check the circuit breaker Go to your home's main electrical panel and find the breaker labeled for the furnace or HVAC system. If it is in the middle (tripped) position, flip it fully to OFF first, then back to ON. Some panels have fuses instead of breakers — check if the furnace fuse is blown and replace it with one of the same amperage.
- Check the furnace power switch Look for a standard light switch on or near the furnace, usually on the side of the unit or on a nearby wall. Make sure it is in the ON position. This switch is easily mistaken for a regular room light switch and may have been turned off accidentally.
- Restore gas and verify power Turn the gas supply valve back to ON (parallel to the pipe) and turn the furnace switch on. Check the furnace control board through the access panel — the LED should now be lit. Set your thermostat to call for heat and confirm the furnace starts.
When to Call a Professional
Contact a licensed HVAC technician if:
- The circuit breaker trips again immediately after resetting
- The power switch is on and the breaker is not tripped, but the LED remains off
- You notice a burning smell or signs of electrical damage near the furnace
- You are not comfortable working around your electrical panel
Frequently Asked Questions
Why is my Bryant 340MAV showing no light on the control board at all?
A completely dark LED means the board has lost power. Most often it is a tripped breaker or a furnace switch left off. If both are fine, an internal transformer or wiring fault needs a technician.
Where is the power switch for my furnace?
It looks like an ordinary light switch mounted on or beside the furnace cabinet, often near the unit or at the top of the basement stairs. It is easy to flip off by mistake.
The breaker keeps tripping when I reset it — what does that mean?
A breaker that trips again right away usually signals a short or a failing component drawing too much current. Stop resetting it and call a technician, since repeated resets can be a fire risk.
✓ Verified against manufacturer service manual — March 2026