A. O. Smith Water Heater A9-17B: Official Meaning and Model Scope
Direct answer
What A9-17B means
The official Cyclone MXi BTH 120-500 Series 300/301 Service Handbook identifies A9-17B as flame sensor detected flame when the gas valve should be off. This record applies only to the documented Cyclone MXi BTH 120-500 Series 300/301 commercial gas water heater.
Search/display variants: A9-17B, A917B
Before you begin
Safety first
This gas water-heater record preserves the manufacturer-stated meaning only. Do not open panels, test live voltage, adjust gas pressure, bypass a safety device, or replace a part from the code alone.
- Record the complete code or exact LED flash pattern before cycling power.
- Confirm the complete rating-label model against the cited service handbook.
- Stop use and leave the area if you smell gas; contact the gas supplier or emergency service from a safe location.
Does this guide apply?
- Region
- United States
- Product family
- Cyclone MXi BTH 120-500 Series 300/301 commercial gas water heater
- Exact models
- Not listed in the cited source. Confirm the full model in the official manual.
- Scope note
- The handbook identifies the Cyclone MXi BTH 120-500 Series 300/301 commercial gas water heater, but does not provide a complete individual-model list. Match the full rating-label model to the handbook before using this code meaning.
Find the model label and official manual before ordering a part
Common paths to check
These are source-backed possibilities, not probability estimates for your specific unit.
- 01 Official handbook meaning: Flame sensor detected flame when the gas valve should be off.
Decision path
Safe checks, in order
- 1
Confirm the display and model
Photograph the complete display or flash sequence and the rating label, then verify that the cited handbook covers the exact model and control type.
Expected: The displayed code and complete model both match the cited handbook.
If not resolved: Contact A. O. Smith support with the model, serial number, code, and handbook link.
- 2
Keep inspection external
Check only for externally visible unsafe conditions such as a gas odor, smoke, soot, water leakage, blocked accessible termination, or a tripped building breaker. Do not restart after an unsafe condition.
Expected: No unsafe external condition is present and no internal access is required.
If not resolved: Stop using the heater and arrange qualified gas-appliance service.
Reset and test
A user reset is not documented for this condition.
Important: No universal reset is asserted. Follow only the exact model handbook after the fault cause has been corrected by a qualified technician.
Escalation point
Stop and arrange service when
- There is a gas odor, flame when the burner should be off, smoke, soot, overheating, sparking, water leakage, or repeated breaker tripping.
- The complete model or control type does not match the cited handbook.
- The official procedure requires panel removal, combustion analysis, live electrical testing, gas-pressure work, or safety-control service.
Model-first repair planning
Components that may be involved
The items below describe the documented diagnostic path. They are not a diagnosis and do not identify a compatible replacement part without the complete model and original part number.
- No replacement part identified without model-specific diagnosis
Official sources
We paraphrase manufacturer material and show the publication scope so you can verify it.
- Cyclone MXi BTH 120-500 Series 300/301 Service Handbook A. O. Smith · PDF page 20, A9-17B error-code entry · accessed 2026-08-09
Reviewed by Device Fix Guide · Last source check:
Related guides for this equipment
These links share the same brand and equipment family. A related guide does not prove that the codes have the same cause on your model.
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