Lennox SLP98UHV Error Code .: Idle Mode
What Does Code . Mean?
The blinking decimal point on the Lennox SLP98UHV display indicates idle mode. The furnace is powered on, the control board is functioning normally, and the system is standing by for a heating or cooling call from the thermostat. The decimal blinks at 1 Hertz — half a second on, half a second off.
This is the normal resting state for the furnace when no heating or cooling is being requested. You will see this display whenever the thermostat is satisfied (room temperature has reached the setpoint), the system is between cycles, or the thermostat is set to OFF. It confirms that the control board has power and is operating correctly.
No action is needed when you see this display. If you expected the furnace to be heating but see the idle display instead, check your thermostat settings to make sure it is set to HEAT and the temperature setpoint is above the current room temperature.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Normal standby — furnace is powered on but not actively heating or cooling | Most common | — |
When to Call a Professional
Contact a licensed HVAC technician if:
- The furnace stays in idle mode when the thermostat is calling for heat and the room is cold
✓ Verified against manufacturer service manual — March 2026