11AO Smith · 310 series condensing tankless · Water Heater

AO Smith 310 series condensing tankless error code 11

Ignition failure, the burner never lit

Stop using it

Which models this applies to. This page covers the AO Smith 310 series condensing tankless gas water heater codes.

What is specific to the 310 series condensing tankless platform

Sealed combustion condensing unit available as direct vent, indoor and outdoor versions. The same two-digit fault numbers apply across the versions, and the fault appears on the control board LED and on the remote controller when one is fitted.

Your control board prints the code as text, for example F01 or EE3, so you read it off the display rather than counting blinks. The printed number is the fault itself, not a position in a table.

Quick answer

On AO Smith 310 series condensing tankless, 11 is a fault. It means ignition failure, the burner never lit. A first thing to check: Gas supply shut off, or the gas valve closed partway, or a supply line that is not connected.

Applies to: AO Smith 310 series condensing tankless; AO Smith 310 series condensing tankless gas water heater codes · Water Heater
Type of code: Fault; Urgency: Stop using it
First safe check: Confirm the gas supply valve is open and that other gas appliances in the home are running, which tells you the supply is live.

Checked 2026-09-26

What 11 means on this model

The gas valve opened and the control commanded a spark three times without ever confirming a flame, so it shut the gas off and stopped trying. The flame never established at all here, which is what separates this code from a loss of flame.

Symptoms you will notice

Code appears after a demand for hot water, three ignition attempts in a row
No hot water at any fixture
A steady clicking or buzzing from the burner compartment during the attempt
Unit goes into lockout and stays there until the breaker is cycled
A short sputter of flame right at the burner, then nothing

Common causes

The code tells you what the control detected, not which part failed. These are the causes we see most often, roughly in order of likelihood:

Gas supply shut off, or the gas valve closed partway, or a supply line that is not connected
Inlet gas pressure outside the range the manual specifies
Soot on the flame rod so the control cannot prove a flame is present
High limit switch open because the heat exchanger is overheated or the fan is not moving air
Open flame current circuit, or an oxidised or broken igniter
Burner or manifold nozzles partly blocked with dust and lint
Heat exchanger leaking, or a flue or vent leak pulling flame away

What you can safely check

These are homeowner-level checks. None of them need you to open a live electrical compartment or work on gas.

Confirm the gas supply valve is open and that other gas appliances in the home are running, which tells you the supply is live.
Hold a propane or natural gas rated detector near the burner compartment, not above it, and confirm it reads gas when the supply is open. If it does, get out and call for help.
Look at the flame rod with a flashlight through the sight glass or inspection port and note any soot or a blistered tip.
Listen during an ignition attempt. No spark at all points to the igniter circuit; a spark with no kick to the valves points to the gas valve circuit.
With power off, check the wiring between the board, the high limit switch, and the gas valve assembly for a break or a burnt end.

Do not do these

×Do not light the burner by hand or hold a lighter or a match to the burner to get hot water. That bypasses the flame supervision and the air proving that make the unit safe.
×Do not keep resetting the unit. Three failed attempts is a designed shutdown and a carbon monoxide protection, not a nuisance to retry.
×Do not clean the flame rod with anything abrasive or wet. A polished or contaminated rod changes the current the control expects and can hide a real fault.
×Do not work on the gas valve or the igniter wiring with power live.

When to call a technician

Stop using the appliance and call today

This one is a safety limit, not a nuisance. The control is shutting the unit down to prevent damage or a hazard, and it will keep doing that until the underlying cause is fixed. Running it anyway risks the expensive failure it was designed to prevent.

This is a fuel-burning appliance, so treat anything involving a burner, gas valve or flue as technician work. If you smell gas at any point, leave the property and call the gas utility from outside rather than continuing to diagnose.
If the appliance has stopped mid-cycle, is making a noise you have not heard before, or smells burnt, stop reading here and call. Those are symptoms of something the fault code does not describe well enough.

Reading the code and confirming gas supply is a homeowner task. Anything on the gas valve, the igniter, or inside the sealed chamber is a licensed gas technician job.

What it costs to fix

Parts

Flame rod $25 to $70. Igniter $60 to $180. Gas valve assembly $150 to $450. High limit switch $30 to $80.

Labor

One to two hours for a flame rod, igniter, or high limit switch. Budget three hours plus the parts cost if the gas valve assembly is being replaced.

DIY or technician