A. O. Smith Water Heater 551: Official Meaning and Model Scope
Direct answer
What 551 means
The official ATIO 910 Service Handbook identifies 551 as abnormal solenoid gas valves. This record applies only to the documented 910 / 910 ASME (T-M50 / T-M50 ASME) on-demand water heater.
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
- 910 / 910 ASME (T-M50 / T-M50 ASME) on-demand water heater
- Exact models
- 910, 910 ASME, T-M50, T-M50 ASME
- Scope note
- The cited service handbook explicitly names 910, 910 ASME, T-M50, T-M50 ASME. Match the complete rating-label model 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: Abnormal solenoid gas valves.
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.
- ATIO 910 Service Handbook A. O. Smith · PDF page 16, 551 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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