State Water Heater E100 Error Code — What It Means
The E100 code on a State tankless water heater signals an ignition failure or no-ignition lockout. The unit attempted to start its burner but could not prove flame during the ignition sequence. This fault is most commonly tied to blocked air intake screens, restricted gas supply, or low water flow through a clogged inlet filter. The heater enters a safety lockout to prevent unburned gas from accumulating.
Common Causes
- Blocked air intake screens Lint, dust, or debris on the combustion air intake prevents the correct air-fuel mix needed for reliable ignition.
- Dirty inlet water filter A clogged inlet screen reduces flow below the threshold required to trigger the ignition sequence.
- Low gas pressure or restricted gas supply Undersized gas line, partially closed valve, or low inlet pressure starves the burner during startup.
- Blocked or improperly installed venting Exhaust obstructions, excessive vent length, or too many elbows create back-pressure that prevents ignition.
- Contaminated flame rod or flame sensor Carbon or mineral deposits on the flame-proving hardware stop the control board from confirming ignition.
Step-by-Step Fix
- Turn off power and gas at the dedicated shutoffs before beginning any inspection or cleaning work.
- Inspect the air intake screen on the front or side of the unit and remove any lint, dust, or blockage with a soft brush or vacuum.
- Remove and clean the inlet water filter at the cold-water connection using a soft brush and running water to clear sediment or debris.
- Verify gas supply: confirm the gas cock is fully open, check that the correct fuel type is connected, and look for any kinks or undersized pipe upstream.
- Check the exhaust vent for obstructions, proper termination clearance, and compliance with the installation manual’s length and elbow limits.
- Clean the flame rod and igniter assembly by removing the burner cover and gently wiping the sensor surfaces with fine sandpaper or a clean cloth.
- Restore power and gas, then test by opening a hot-water tap and watching for normal ignition. If E100 returns, note the symptom and call a qualified technician for combustion diagnostics.
Parts Often Needed
| Part | Notes |
|---|---|
| Inlet water filter screen | Amazon | Original State or A. O. Smith part matched to your model’s inlet connection size. |
| Flame rod and igniter assembly | Amazon | Required when cleaning does not restore reliable flame sensing. Verify part number from your model label. |
| Air intake and vent pipe kit | Amazon | Use only if the existing vent system is damaged, improperly sized, or does not meet current installation codes. |
When to Call a Pro
Call a licensed plumber or gas technician if the E100 code persists after you have cleaned the air intake, inlet filter, and flame rod. Diagnosing low gas pressure, testing ignition voltage, adjusting combustion air settings, or replacing the gas valve or control board requires specialized tools and training. Ignition faults that recur after basic cleaning often point to improper venting, incorrect gas piping, or a failing ignition module that must be tested under load by a qualified professional.