Lennox furnace Alert code 349: O to R jumper cut on the furnace control
Alert 349 means the O to R configuration link on the furnace control has been cut. Lennox warns it can cause a brown out and low voltage, and the fix is to restore the link by hard-wiring R to O at the terminal strip.
Applies to: Lennox gas furnaces running in non-communicating mode. Lennox states this alert is only applicable in non-communicating mode.
What it means
The O terminal is the reversing valve signal used with a heat pump. On a furnace configured for non-communicating operation, Lennox uses a factory link between R and O that has to be present unless the installation specifically requires it cut. When it has been cut and not restored, the control reports 349. The reason this matters more than a configuration nag is what Lennox says it can cause: a brown out, and low voltage that will generate further alert codes of its own. So a furnace showing 349 alongside voltage alerts is not necessarily suffering two faults — the second may be downstream of the first, and chasing the voltage codes first would be chasing a symptom.
Most common causes
- The R to O link cut during installation for a heat pump configuration and never restored when the configuration changed.
- The link cut in error during setup.
- A control board replaced without the link being reinstated to match the installation.
- A system converted from dual fuel to gas-only without the configuration being reverted.
How to diagnose it
- Note whether the system is running in non-communicating mode — Lennox says the alert applies only there.
- Check the fault history for low voltage alerts alongside this one; Lennox links the two directly.
- Note whether the system was recently converted, reconfigured, or had a control board replaced.
- The terminal strip is inside a live cabinet, so the check itself is technician work.
How to fix it
- Restore the configuration link by hard-wiring the R and O terminals on the terminal strip, which is Lennox's stated remedy.
- Resolve this before investigating any accompanying voltage alerts, since Lennox says this fault can generate them.
- If the installation genuinely requires the link cut, the configuration and the mode need to be made consistent rather than the alert dismissed.
Notes
This is a configuration fault rather than a failure, which makes it one of the more satisfying codes on the list — nothing is broken, and the remedy is a wire.
Related
All codes for this manufacturer
Lennox furnace alert codes — every code, with what differs between models.