State Water Heater E166 Error — What It Means
State Water Heaters (a brand of A.O. Smith) does not list E166 as an official error code in any public manual, support database, or authorized reference. State units typically display codes like 11, 12, 14, 24, 65, E001, E003, E012, E030, and E110, but E166 does not appear in known catalogs. This suggests the code may be misread (for example E110 seen as E166), may be a custom diagnostic on a specific unreleased model, or could indicate a control-board glitch that requires manufacturer clarification.
Because no public documentation exists for E166, attempting repairs based on guesswork can waste money and create safety risks. The safest course is to verify the exact code on the display, attempt a power reset, and contact State Water Heaters technical support using the QR code on the rating plate or by providing your model and serial number. If the code persists after a reset, the issue may involve internal components such as the main control board, vent blockage sensors, or ignition circuitry that require professional diagnosis.
Before You Replace Anything
Without a confirmed meaning for E166, technicians may replace the main control board or flame sensor unnecessarily. Always verify the exact code and consult State support before ordering parts.
Common Causes
- Misread error code (~40%) The display may show E110 or another documented code that looks like E166 from an angle or due to a partial segment failure.
- Control board glitch (~25%) A transient firmware or memory fault may generate an undocumented code that clears after a power cycle.
- Proprietary diagnostic on a specific model (~20%) Some newer or commercial State units may use internal codes not published in homeowner manuals.
- Vent or air-intake blockage triggering an unlisted fault (~10%) Blockages can cause pressure-switch or ignition faults that the board logs as a non-standard code.
- Failed main control board (~5%) A failing PCB may display random or invalid codes before complete failure.
Quick Diagnosis
Answer these to narrow it down fast.
Does the display clearly show E166, or could it be E110 or another code?
No: Look up the correct code in your owner's manual and follow the documented troubleshooting steps.
Does the code clear after unplugging for one minute and reconnecting?
No: The fault is persistent. Check air intakes and vents for blockages, then contact State support or a licensed contractor.
Are the air intake screens and vent pipes free of lint, ice, or debris?
No: Clear the blockage and reset the unit. If the code persists, the blockage may have damaged a pressure switch or other component.
Step-by-Step Fix
- Write down the exact code displayed, including all digits and letters, and take a photo of the screen if possible.
- Unplug the water heater from power (or turn off the dedicated circuit breaker) and wait one full minute before reconnecting.
- Restore power and observe whether the code reappears or if the unit attempts normal startup.
- Inspect air intake screens on the unit exterior and remove any lint, pet hair, or debris by hand or with a soft brush.
- Check vent pipes for obstructions such as ice, bird nests, or disconnected sections, especially in cold weather.
- Locate the rating plate on the side of the unit and scan the QR code or note the model and serial number for technical support.
- Contact State Water Heaters support directly to confirm whether E166 is a valid code for your model and to receive model-specific diagnostics and next steps.
Parts Often Needed
| Part | Notes |
|---|---|
| Main Control Board (PCB) | Amazon | Only order after State support confirms E166 points to a board fault for your specific model. |
| Air Intake Screen | Amazon | Replace if damaged or heavily clogged and cleaning does not restore airflow. |
When to Call a Pro
Call a licensed plumbing or HVAC contractor immediately if the E166 code persists after a power reset and you cannot verify the code in your manual. Because State does not publicly document E166, professional diagnosis is necessary to avoid wasting money on incorrect parts or creating carbon monoxide hazards from misdiagnosed vent blockages. A qualified technician can test gas pressure, inspect the flame rod, measure inducer motor voltage, and communicate directly with State technical support using your model and serial number. Do not attempt internal repairs or part replacement without confirmed fault data, especially if the unit involves gas combustion or high-voltage components.
Rough cost: A pro service call runs about $150-350.