Lennox SLP98UHV Error Code h: Variable Capacity Heat Display
What Does Code h Mean?
On this modulating SLP98UHV, the h item in the SureLight control's menu reports how hard the furnace is currently firing. The LED shows a lowercase h together with the percentage of full input rate and the blower CFM the board has matched to that rate.
Because the SLP98UHV modulates rather than running only on/off, this percentage is meant to rise and fall continuously as your home's heat demand changes. A low percentage is not a problem — a modulating furnace deliberately runs at a reduced rate to hold a steady temperature efficiently, stepping up only when the home falls further behind the setpoint. This differs from the uppercase H readout, which shows the discrete heat stage (1 or 2) and its airflow rather than the live firing percentage.
No action is required. The readout reflects normal operation and clears when the diagnostic menu times out or the heat call ends.
What You'll Notice
- The LED shows a lowercase h together with a percentage (the current input rate) and a CFM value for the blower.
- The furnace is heating normally while this displays, and the numbers rise and fall as it modulates up or down.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Diagnostic push button pressed to view variable capacity heat settings | Most common | — |
How This Is Diagnosed
Because the SLP98UHV modulates, the percentage shown reflects normal up-and-down changes in firing rate rather than a problem. Confirm this by letting the diagnostic menu time out or by watching that the furnace keeps warming the home; if heat is being delivered, the h readout is doing exactly what it should.
- The furnace stays pinned at a low percentage and never steps up even though the home is not reaching the setpoint
- You hear unusual noises or the home will not warm while this readout is active
Frequently Asked Questions
What does the percentage next to 'h' mean?
It is the furnace's current firing rate as a percentage of its maximum input. Because the SLP98UHV modulates, this number naturally varies with how much heat your home needs.
Is a low percentage a problem?
Not by itself. A modulating furnace often runs at a low rate to hold a steady temperature efficiently. It is only a concern if the home never reaches the setpoint.
How do I clear the h readout?
It is not a fault, so there is nothing to clear. It disappears when the diagnostic menu times out or the heat call ends.
✓ Verified against manufacturer service manual — March 2026