A.O. Smith water heater faults: fault codes, causes and parts
All 231 fault codes for A.O. Smith water heaters, plus the faults that show no code. Type your code or choose your symptom.
A fault on an A.O. Smith water heater usually means that the appliance has locked out or is reporting a fault code. Note the code on the display and look it up below: for each code you will find its meaning, checks you can safely do yourself and the parts that are often checked or replaced. Frequently searched: F04 (three unsuccessful ignition attempts), Max. burner hours: service (the actual burner hours are higher than…), Anode protection not working (the boiler is working, but the anode…). No code? Check the power supply, the settings and the filters, and reset once. If the fault comes back, call in a qualified professional.
Most searched A.O. Smith faults
These are the codes that visitors to this site search for most often.
See the 25 most searched fault codes of 2026, with the figures behind them →
A.O. Smith water heater faults without a code on the display
Not every fault shows a code. These are the symptoms we come across most often with A.O. Smith appliances, with what you can check yourself before calling someone out.
No or too little hot water
Check the set temperature and whether the appliance has power. On an electric water heater, the most common cause is a burnt-out heating element or a tripped high-limit thermostat. View the matching parts → Read the full explanation: water heater not producing hot water →
Water gets too hot
Usually a thermostat that no longer regulates properly. Switch the appliance off and have the thermostat checked; water that is too hot is a scalding risk. View the matching parts → Read also: heating element, thermostat or limescale? →
Water under the water heater
Check whether it is coming from the pressure relief valve (a little during heating is normal) or from the tank itself. If the tank is leaking, replacement is the only solution. View the matching parts →
Limescale or brown water
A tank that has not been serviced for years collects limescale, and the anode is then often used up. Replacing the anode in good time considerably extends the life of the tank. View the matching parts → Read the full explanation: replacing the anode →
A.O. Smith water heater fault codes 1 to 150 of 231
The code list is split over 2 pages. Looking for a specific code? Use the search at the top of this page: it searches all 231 codes in one go.
Order parts for your A.O. Smith water heater
A.O. Smith parts are available from Instalpunt; shipping to EU countries from €12.95 (€16.95 for more distant countries), usually 3–5 working days.
Frequently asked questions about A.O. Smith faults
What does a fault on an A.O. Smith water heater mean?
The appliance is reporting that it has shut itself down or cannot continue. The code on the display points to the group of causes: ignition, water pressure, a sensor, the fan or communication with the thermostat. The table above shows, for each code, what A.O. Smith means by it.
How do I reset my A.O. Smith water heater?
The reset button is on the control panel of your A.O. Smith water heater; on most appliances you hold it down for two to five seconds until the display responds. Reset once. If the same fault comes straight back, resetting will not solve it and a part or a setting needs attention. Always consult the manual for your model: the position of the button and how long to press it differ per series.
Can I fix an A.O. Smith fault myself?
You can top up the water pressure, bleed the system, replace filters and clean a siphon yourself. Anything behind the sealed section of a gas appliance is a different matter: work on the gas valve, burner, heat exchanger and flue must be carried out by a certified gas engineer.
How much does it cost to fix a fault?
That depends on the cause and whether a part is needed. With us you can see the part straight away with its price and delivery time, so you know where you stand in advance. If you call in an engineer, always ask about the call-out charge and hourly rate before they come.
Where can I find the right part for my A.O. Smith?
Check the rating plate for the exact type and use it to search our catalogue, or search directly by the manufacturer number of the faulty part. Each part lists the appliances it fits.