AO Smith 310 series condensing tankless error code 03
Dipswitch setting does not match the installation
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, 03 is a fault. It means dipswitch setting does not match the installation. A first thing to check: Altitude dipswitch still set for sea level at a high-elevation site.
- 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: Needs attention soon
- First safe check
- Write down which gas the unit is actually connected to before touching any switch.
What 03 means on this model
The configuration switches on the control board do not match how the unit is installed. Gas type, altitude and the venting arrangement are all set with these switches, and the control reads them at power-up, so a wrong setting stops the unit before it heats anything.
Symptoms you will notice
- Code appears the moment power is restored, before any hot water is drawn
- Unit never advances past startup, hot water stays cold
- Code returns every time the breaker is reset
- Unit was moved, re-piped, or re-vented recently and the fault started then
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:
- Altitude dipswitch still set for sea level at a high-elevation site
- Gas type switch set to natural on a unit piped for propane, or the reverse
- Venting configuration switches left in a factory default after a field change
- Switch moved by vibration, debris, or a knocked cover during service
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.
- Write down which gas the unit is actually connected to before touching any switch.
- Confirm the gas type printed on the rating plate matches the supply, then compare it to the switch position.
- Note the elevation of the install site and confirm the altitude range the switch is set for covers it.
- With power off, look at the switch bank on the board and see whether any switch sits between its two positions.
Do not do these
- ×Do not change dipswitches on a live board. Power off at the breaker and confirm the board is dead before touching a switch.
- ×Do not set the gas type switch to match the gas the building has without confirming the unit is rated for it. A wrong-gas setting on an appliance it is not rated for is a safety problem, not a configuration fix.
- ×Do not use this fault as a reason to keep bypassing the control. The switch settings are how the appliance knows its own installation conditions.
When to call a technician
Book a technician, do not keep resetting it
This fault will not clear on its own. Every power cycle gives the control one more failed attempt, and repeated attempts are what turn a cheap part replacement into a seized or contaminated system.
- 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 fault and setting the switches is straightforward for someone comfortable identifying the gas type. Because the switches include gas type and altitude, an incorrect setting is a carbon monoxide risk, so have a technician confirm the result on a new install.
What it costs to fix
Parts
None for a settings correction. Board replacement $150 to $350 if a switch bank has been damaged.
Labor
Twenty minutes to read and set the switches. Add an hour if the board has to come out to reach them.
DIY or technician
Reading the fault and setting the switches is straightforward for someone comfortable identifying the gas type. Because the switches include gas type and altitude, an incorrect setting is a carbon monoxide risk, so have a technician confirm the result on a new install.
Typical US part and labor ranges, 2026. They vary by region, model and contractor, so treat them as a planning figure, not a quote.
Scope of this code
- Code table
- AO Smith 310 series condensing tankless gas water heater codes
- How this model reports the code
- Printed on the control display
- Models in scope
- AO Smith 310 series condensing tankless
- How this platform differs
- 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.
- Checked
- Confirm on your own unit
- Find the model number on the data plate, then check this code in the service manual for that model. Manufacturers revise code tables between model years, and a revised board can renumber a fault.