Lochinvar Boiler Equipment & Error Codes

Platform & Control Notes

Knight boilers with the SMART SYSTEM / SMART TOUCH control display text fault MESSAGES (e.g. 'No Flame Ign', 'Fan Low'), not numbered codes. Exact wording varies by firmware/model year.

Model Families & Platforms

• Knight Series (WHB / WB high-efficiency condensing)
• Noble Series (Combi fire-tube)
• FTXL & Armor (Commercial condensing platforms)

Diagnostic Characteristics & Common Service Topics

Lochinvar boilers utilize specific display codes and safety lockouts to protect the heat exchanger, combustion system, and hydronic loop. Everyday issues like pressure loss, flame sensing errors, or circulator faults trigger specific responses depending on the controller generation.

Sample Fault Code Summaries from Vault Records

Code	Meaning	Action Required
No Flame Ign	Ignition failure / lockout — failed to prove ignition after four attempts.	Confirm gas is on and press RESET once. If it lights and stays lit, monitor. Don't repeatedly reset a gas-ignition lockout — if it relocks, call a pro to check electrode, gas pressure, venting, and gas valve.
No Flame Running	Flame loss — boiler was running and lost the flame signal four straight times, then locked out.	Press RESET once and watch whether it stays lit. Recurring flame loss is a gas/combustion issue — call a qualified tech. Don't keep resetting.
Gas Pressure SW	A manual-reset low- or high-gas-pressure switch has tripped.	Verify the building gas valve is fully on and other gas appliances work, then press RESET once. Gas-pressure measurement/adjustment must be done by a pro with a manometer.
Flow Switch/LWCO	Flow switch or low-water cutoff isn't detecting adequate flow/level.	Check that system pressure is adequate (~12+ psi) and listen for the circulator. Bleeding air, fuses, and pump diagnosis should be done by a tech.
APS Open	Air pressure switch open — control isn't seeing proper combustion-air/draft proving.	Flue/combustion-air system — call a tech. Homeowners can confirm exterior intake/exhaust aren't blocked by snow, ice, leaves, or nests; internal diagnosis is a pro job.
Auto Reset High Limit	Outlet water temperature exceeded the high-limit setting.	Confirm pressure is normal and the circulator runs. Low-flow/overheat conditions and sensor/pump replacement should be handled by a tech, especially if it recurs.
Fan Low / Fan High	Combustion-fan RPM is ~30% lower or higher than commanded.	Call a tech to inspect fan, wiring, and venting. Homeowners can check that exterior vent/intake terminations are clear.
GV/Relay Fail	The control board did not detect the gas valve.	Gas-valve fault — call a qualified technician. Not a homeowner repair.

Related Symptom & Diagnostic Guides

Sources & Documentation

• error-codes.json — https://www.lochinvar.com/lit/KB-SER-08.pdf