State Water Heater E15 Error Code — What It Means
On State tankless condensing water heaters (manufactured under A. O. Smith), the E15 error code indicates a venting or airflow restriction that prevents the unit from establishing or maintaining proper combustion. The heater is shutting down because it cannot draw enough intake air or vent exhaust gases correctly. In most State and A. O. Smith tankless models, this fault is tied to blocked air intake screens, restricted vent terminations, or improper vent assembly rather than a component failure inside the unit.
Common Causes
- Blocked air intake screens Lint, dust, insects, or debris clog the intake louvers or screens, starving the burner of combustion air.
- Restricted or blocked exhaust vent termination The exterior vent cap or termination is obstructed by leaves, nests, ice, or other debris, preventing exhaust gases from exiting.
- Improper or damaged vent piping Vent runs are disconnected, crushed, sagging, or installed with too many bends, restricting airflow through the system.
- Insufficient gas supply or gas-line restriction Low gas pressure or a partly closed valve mimics combustion-airflow faults by preventing stable ignition.
- Low water flow or dirty inlet filter A clogged inlet screen reduces flow enough to trigger related ignition and combustion faults on some tankless models.
Step-by-Step Fix
- Lock out electrical power and turn off the gas supply at the appliance shutoff valve before inspecting or disassembling any components.
- Inspect the air intake path first. Remove and clean intake screens, louvers, and any accessible intake ducting, checking for lint, leaves, insect nests, or other blockage.
- Check the exhaust vent termination outside the building for obstructions, verify all vent piping is intact and properly supported, and confirm no sections are crushed or disconnected.
- Verify gas supply pressure and flow at the appliance if airflow checks are clear, because low gas delivery can produce the same fault family.
- Remove and clean the inlet water filter if your model includes one, especially if the unit has been displaying low-flow faults or the filter appears dirty.
- Restore power and gas, then reset the unit and monitor a full heating cycle to confirm normal ignition and stable combustion without the fault returning.
- If the E15 code reappears immediately, stop resetting and call a qualified technician to diagnose combustion components, the fan, flame sensor, and control board rather than cycling the fault repeatedly.
Parts Often Needed
| Part | Notes |
|---|---|
| Air intake screen assembly | Amazon | Replace if clogged beyond cleaning or physically damaged. |
| Vent termination cap and piping | Amazon | Use manufacturer-approved vent components; incorrect materials or fittings can create new restrictions. |
| Inlet water filter | Amazon | Replace if the mesh is torn or mineral buildup cannot be flushed clean. |
When to Call a Pro
Call a licensed plumber or gas technician if you have cleared all visible intake and exhaust blockages and the E15 fault persists, if you are uncomfortable working with gas piping or verifying gas pressure, or if the vent system requires disassembly inside walls or ceilings. Repeated fault codes after clearing obstructions point to a combustion-component issue (fan, flame sensor, igniter, gas valve, or control board) that requires meter diagnostics and model-specific repair procedures. Always call a professional for any work involving gas connections, combustion testing, or control-board replacement.