State Water Heater E158 Error — What It Means
The E158 error code does not appear in State Water Heater (A.O. Smith brand) official service manuals or diagnostic databases. State tankless units typically use numeric codes (11, 12, 16) or A.O. Smith alphanumeric codes (E001 through E030). E158 may be a misread display, a code from a different brand (Noritz, Navien, Rheem, or Rinnai), or a custom diagnostic code for a specific State model not widely published.
If your unit is showing an ignition-related failure or flame loss, the most common culprits in State/A.O. Smith tankless systems are air intake blockages, low gas flow or pressure, clogged inlet water filters, and scale buildup on the heat exchanger or flame rod sensor. Verify the exact code in your owner’s manual or on the wiring diagram inside the service panel before starting diagnostics.
Before You Replace Anything
Homeowners often replace the flame rod sensor when the real problem is a clogged air intake screen or dirty inlet filter. Clean both filters first and power-cycle the unit before ordering any parts.
Common Causes
- Air intake screen clogged (~40%) Lint, debris, or ice on the intake screen blocks combustion air and prevents ignition or causes flame loss.
- Inlet water filter dirty (~25%) A clogged inlet filter reduces water flow below the minimum threshold needed to activate the burner.
- Flame rod sensor fouled (~20%) Scale and carbon buildup on the flame rod prevent it from detecting the flame, triggering a safety shutoff.
- Exhaust vent blocked (~10%) Snow, ice, or debris in the vent pipe creates back-pressure and shuts down combustion.
- Low gas pressure or incorrect gas type (~5%) Improperly adjusted manifold pressure or using the wrong gas (propane vs. natural gas) prevents stable ignition.
Quick Diagnosis
Answer these to narrow it down fast.
Is the air intake screen free of lint, ice, or debris?
No: Clean the screen thoroughly. Power-cycle the unit and test. This solves most ignition errors.
Does the unit attempt to ignite (you hear a clicking or see a spark) but fail to light or stay lit?
No: The unit may not be getting water flow or power. Check the inlet filter and electrical connections.
Is the exhaust vent and termination clear of ice, snow, or obstructions?
No: Clear the blockage immediately. Vent obstructions can cause carbon monoxide hazards and combustion failure.
Step-by-Step Fix
- Turn off power to the water heater at the breaker or unplug the unit.
- Remove and clean the air intake screen by pulling it out and rinsing under water or brushing away lint, debris, and ice.
- Inspect the exhaust vent termination outside your home and clear any snow, ice, or blockages from the pipe opening.
- Remove and rinse the inlet water filter located on the cold-water supply line entering the unit to restore full flow.
- Clean the flame rod sensor by accessing the combustion chamber (consult your model’s service manual), gently wiping the rod with a soft cloth or fine brush to remove scale and carbon deposits.
- Verify gas supply by confirming the gas valve is fully open and checking that other gas appliances in the home are working normally.
- Power-cycle the unit by unplugging it (or switching off the breaker) for 20 seconds, then restoring power to reset the control board and clear temporary faults.
Parts Often Needed
| Part | Notes |
|---|---|
| Flame rod sensor (State/A.O. Smith tankless) | Amazon | Match your exact model number. Often fouled by scale or carbon rather than failed. |
| Inlet water filter screen | Amazon | Generic mesh screen or OEM part. Check thread size and micron rating for your model. |
| Air intake screen kit | Amazon | OEM replacement if original is damaged. Most can be cleaned and reused. |
When to Call a Pro
Call a licensed plumber or gas technician if the error persists after cleaning the air intake, inlet filter, and flame rod. Professional diagnostics are needed for gas valve replacement, manifold pressure adjustment, heat exchanger descaling, or if the unit repeatedly shuts down with ignition failures. Gas work and sealed combustion systems require certification and special tools. Also call if you smell gas, see visible corrosion on the burner assembly, or if the unit is still under warranty (DIY repairs may void coverage).
Rough cost: DIY runs about $15-50 in parts, 20-45 min. A pro service call runs about $150-300.