Lennox SLP98UHV Error Code H: Heat Stage Display
What Does Code H Mean?
The uppercase letter H in the SureLight control's menu reports the heat-stage configuration. Cycling the diagnostic push button brings it up, and the LED shows the heating stage number (1 or 2) followed by the CFM setting for that stage before repeating.
Even though the SLP98UHV modulates its output, the board still defines discrete stage boundaries: Stage 1 covers the lower range of heating output used for milder demand, and Stage 2 the higher range for cold weather, with blower speed matched to each so airflow across the heat exchanger stays correct. Do not confuse this with the lowercase h readout, which reports the live variable-capacity firing percentage rather than the stage setting.
This is an informational display and needs no action. Technicians use it to verify the heating configuration is correct for the installed system, and it cycles on to other diagnostic items or returns to idle by itself.
What You'll Notice
- The LED shows an uppercase H followed by a heating stage number (1 or 2) and then a CFM value, repeating.
- Whatever the furnace was doing continues unchanged while the readout cycles.
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Diagnostic push button pressed to view heat stage settings | Most common | — |
How This Is Diagnosed
Confirm this is a configuration readout, not a fault, by noting it appears only while the diagnostic push-button menu is open. Allow the menu to advance past the H entry — items change every five seconds — or wait for it to return to idle; the resumed normal display confirms nothing is wrong.
- You suspect the heating stages or their blower speeds were not set correctly for your home
- Heating comfort is poor and you want the stage configuration checked
Frequently Asked Questions
What's the difference between 'H' and 'h' on my furnace?
Uppercase H is the heat-stage readout (stage 1 or 2 plus its airflow), while lowercase h reports the live variable-capacity firing percentage. Both are diagnostic displays, not errors.
Is uppercase H an error?
No. It is a technician readout of the heating stage settings, shown deliberately through the diagnostic button.
Will the H display go away on its own?
Yes. When you stop cycling the diagnostic menu, it times out and the display returns to normal.
✓ Verified against manufacturer service manual — March 2026