Lennox SLP98UHV Error Code E 331: Communication Link Problem
What Does Code E 331 Mean?
Error code E331 on the Lennox SLP98UHV indicates a communication link problem on the global network connection. In the Lennox documentation this code is designated "for future use" — it is reserved in the system architecture and does not necessarily represent an active fault on a given installation.
Because it is a reserved code, E331 is frequently ignorable when the system is running normally. If your furnace is heating and cooling on demand, the iComfort thermostat is responsive, and there are no comfort complaints, this code is typically informational rather than a sign that something is broken. It differs from the active communication-bus faults in this series — such as E105 (no devices detected on the bus), E120 (a device on the bus that was slow to respond), or E124 (the communicating thermostat signal missing for more than three minutes) — which describe specific, diagnosable communication failures. E331 is a reserved link code that is often benign.
That said, if you are also seeing actual communication problems, the code is worth mentioning to your technician so the communicating wiring and device compatibility can be checked as part of the visit.
What You'll Notice
- E 331 shown in the furnace control's error code recall menu
- The system otherwise heats and cools normally with a responsive thermostat
- No lockout, no loss of heat, and no comfort complaints in a typical case
Common Causes
| Cause | Likelihood | DIY? |
|---|---|---|
| Communication link failure between system components on the network | Most common | ✗ Call a pro → |
How This Is Diagnosed
Because E331 is a reserved code that often clears on its own, a homeowner can safely cycle power at the breaker to see whether it disappears, then confirm the system is heating, cooling, and responding to the thermostat normally. If everything works, the code is generally treated as informational and simply noted for the next service visit.
If real communication symptoms accompany the code, a technician evaluates it alongside the active bus codes: checking the communicating wiring between the furnace, thermostat, and outdoor unit, verifying that every device on the network is compatible and correctly configured, and confirming there are no loose or damaged connections. On its own, with a normally running system, E331 usually needs no repair.
When to Call a Professional
This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:
- The code appears together with actual communication problems such as an unresponsive thermostat or outdoor unit
- The code returns after cycling power at the breaker and the system is not running normally
- Zone control or coordinated staging is not working as expected
- You want the reserved code reviewed and logged at your next service appointment
Frequently Asked Questions
Can I ignore E331?
If your furnace is heating and cooling normally and the thermostat is responsive, E331 is usually safe to ignore because it is a reserved "for future use" code. It is still worth mentioning at your next service visit so it can be documented.
How is E331 different from the other communication codes?
Codes like E105, E120, and E124 describe specific, active communication failures on the data bus. E331 is a reserved link code that often does not correspond to a real fault, which is why it is frequently benign when the system runs normally.
Should I be worried if it keeps showing up?
Not necessarily. A persistent E331 on an otherwise normally operating system is usually informational. If it appears alongside genuine communication issues, however, a technician should check the communicating wiring and confirm all networked devices are compatible.
✓ Verified against manufacturer service manual — March 2026