Lennox SLP98UHV Error Code E 349: No 24V Between R and O
What Does Code E 349 Mean?
The Lennox SLP98UHV can control an outdoor heat pump directly. In non-communicating mode, the SureLight Variable Capacity Integrated Control relies on a hard-wired link between the R and O terminals so the O output can drive the heat pump's reversing valve. E 349 means the control found no 24 volts between R and O, which indicates that this R-to-O jumper has been cut or was never installed.
Beyond disabling correct heat-pump changeover, a missing R-to-O link can pull down the low-voltage supply. Lennox notes this condition may cause a brown-out and can generate low-voltage alerts as well, so E 349 sometimes shows up next to voltage-related complaints rather than by itself.
E 349 is one of the non-communicating relay-output family of faults. It sits alongside E 347 (no 24-volt output on Y1 to C, the first-stage cooling relay) and E 348 (no 24-volt output on Y2 to C, the second-stage cooling relay). The fix is to restore the connection by hard-wiring the R and O terminals on the terminal strip, which is board and wiring work for a technician.
What You'll Notice
- The heat pump heats when it should cool, or cools when it should heat (reversed operation)
- The reversing valve does not switch over when the thermostat changes modes
- Low-voltage or brown-out alerts appear along with E 349
- Comfort problems began right after a new install or a service visit
- The outdoor heat pump behaves inconsistently between heating and cooling calls
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| R to O jumper link was cut or removed during installation or service | Most common | ✗ Call a pro → |
How This Is Diagnosed
A technician confirms the system is actually configured as a non-communicating heat pump, since E 349 only applies in that mode. Homeowner-safe checks such as verifying the thermostat mode are fine, but the terminal-strip work belongs to the pro.
They inspect the R and O terminals on the furnace control for a missing or cut jumper and meter for 24 volts between them. If the link is absent, they restore it by hard-wiring R to O per Lennox's instructions, then verify the reversing valve switches correctly and that the low-voltage supply is no longer being dragged down.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The heat pump runs in the wrong mode (heating on a cool call or vice versa)
- E 349 appears together with low-voltage or brown-out alerts
- The problem started right after installation or a service visit
- The R-to-O jumper on the terminal strip needs to be restored
Frequently Asked Questions
What is the R-to-O jumper on my Lennox SLP98UHV?
It is a wire link between the R and O terminals on the control board. In non-communicating mode it lets the O output power the heat pump's reversing valve. E 349 means that link is missing or cut.
Why did E 349 appear right after installation?
The R-to-O link is easy to leave off or accidentally cut during wiring. If it was never restored, the control reports E 349 the first time it needs the heat-pump changeover circuit.
Could E 349 be causing my low-voltage warnings too?
Yes. Lennox notes the missing R-to-O link can pull down the 24-volt supply and cause a brown-out, which may trigger low-voltage alerts alongside E 349.
✓ Verified against manufacturer service manual — March 2026