Carrier 59SC5A Error Code 11: No Previous Code
What Does Code 11 Mean?
Status code 11 (one short flash followed by one long flash) reports that the Carrier 59SC5A control board has no stored fault in its diagnostic memory. The HK42FZ036 retains the most recent status code so a technician can retrieve it later during troubleshooting, and code 11 simply means that memory is clean.
The board erases stored codes automatically after 72 hours. So if a transient event occurred, such as the pressure switch briefly opening during a high-wind gust, its code would be held for three days and then cleared. Seeing code 11 after that window is expected behavior, not evidence that nothing ever happened.
This makes code 11 most useful as a baseline during a code recall. If you deliberately retrieve stored codes and get 11, it confirms that no fault has been logged since the last automatic memory clear, which helps distinguish a truly healthy furnace from one whose fault simply aged out of memory.
What You'll Notice
- During a code recall, the LED shows one short flash then one long flash and no other fault codes
- The furnace is otherwise running normally with no active complaint
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| No faults have occurred in the last 72 hours | Most common | — |
How This Is Diagnosed
Code 11 is read during an intentional recall rather than during a fault. A technician (or a homeowner following the manual) triggers the recall, and the board displays the most recent stored code; code 11 confirms the memory holds no fault. Because codes clear after 72 hours, an 11 does not rule out an intermittent problem that occurred earlier and aged out. When a furnace has symptoms but returns code 11, the next step is to reproduce the fault or monitor the system live so a fresh code can be captured.
- The furnace has intermittent problems that seem to clear before a code can be captured, so a technician may need to monitor it in real time
- You retrieve code 11 but the furnace is still misbehaving, indicating the fault aged out of memory
Frequently Asked Questions
Is code 11 on a Carrier 59SC5A a problem?
No. Code 11 means no fault is stored in the board's memory. It is a normal diagnostic result.
My furnace acted up yesterday but now shows code 11. Why?
The board clears stored codes automatically after 72 hours, but a code that old should still appear. If it is already gone, the event may have been very brief or the memory was reset by a power interruption; try to capture the fault while it is happening.
How do I read stored codes on this furnace?
The 59SC5A supports a code recall using the control's diagnostic procedure in the manual. During recall the board flashes the last stored status code, and code 11 means the memory is clean.
✓ Verified against manufacturer service manual — March 2026