Lennox SLP98UHV Error Code .: Idle Mode
What Does Code . Mean?
A single decimal point pulsing on the 7-segment LED is the SLP98UHV's idle indication. The furnace is powered, the SureLight Variable Capacity Integrated Control has finished its checks, and the system is simply standing by for a heating or cooling request. The decimal blinks at 1 Hertz — about half a second on and half a second off.
This is the normal resting state whenever no call is active: the thermostat is satisfied and the room has reached its setpoint, the system is between cycles, or the thermostat is set to OFF. Because this is a communicating iComfort system, the board stays awake and in constant contact with the thermostat even while idle, which is why the display keeps blinking rather than going dark.
Nothing needs to be done when you see this. If you expected heat but the decimal keeps blinking, the board is telling you it has simply not received a call — the next step is at the thermostat, not the furnace.
What You'll Notice
- A single decimal point on the 7-segment LED blinks steadily about once per second, with no letters or numbers showing alongside it.
- The furnace is silent and the blower is off, yet the control board still has power and starts a normal cycle the next time the thermostat calls.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Normal standby — furnace is powered on but not actively heating or cooling | Most common | — |
How This Is Diagnosed
Confirm this is normal standby by raising the thermostat a few degrees above room temperature with the mode set to HEAT. Within a minute or two the blinking decimal should give way to the ignition sequence and the furnace should start; if it does, the idle decimal was only the resting state and nothing is wrong.
- The decimal keeps blinking and the furnace never starts even though the thermostat is set to HEAT with the setpoint well above room temperature
- You have confirmed the thermostat has power and the correct mode, but no heating or cooling cycle ever begins
Frequently Asked Questions
Is the blinking dot on my Lennox furnace a problem?
No. A single decimal point blinking about once per second is the SLP98UHV's normal idle indication. It means the control board is powered and waiting for the thermostat to call for heating or cooling.
Why is my furnace showing a dot instead of heating?
The dot means no call for heat is currently active. Check that the thermostat is set to HEAT and the setpoint is above the current room temperature; once it calls for heat, the furnace starts and the display changes.
Should I try to clear the idle decimal?
There is nothing to clear — it is a normal state, not a fault. It disappears on its own the moment the furnace begins a heating or cooling cycle.
✓ Verified against manufacturer service manual — March 2026