On the covered AO Smith gas water heater, 5 flashes means sensor failure, which A. O. Smith lists for the temperature sensing inside the gas control. First, notice whether the water is lukewarm, cold or hot, and write down the five-flash pattern.
Differential
Likely causes of “AO Smith gas water heater code 5 flashes”, and how to tell them apart
- 1
The water temperature sensor reads out of range
What separates it Five flashes and little or no heating
How to confirm A. O. Smith words five flashes as a sensor failure
- 2
A sensor wire that has loosened at the control
What separates it Intermittent heating or flashes after the heater was moved
How to confirm A plumber inspects the wiring
- 3
Scale or sediment around the sensor
What separates it Water that runs lukewarm for months before the code
How to confirm A flush may be part of the service
- 4
A control that cannot read a good sensor
What separates it The sensor tests well but the code stays
How to confirm Replace the gas control valve and thermostat
- 5
A heater with a defect from new
What separates it The code appears in the first weeks
How to confirm Claim under warranty
Before you touch a setting
Record this first — changing settings destroys the evidence
- That the status light flashes five times
- Whether the water is lukewarm, cold or hot
- The heater's age and the date on its label
- Whether the heater lights at all
Try in this order
0 of 8 completedWhat to do first
ReversibleNotice whether the water is lukewarm, cold or hot, and write down the five-flash pattern.
Correct only the documented fault domain
ReversibleA. O. Smith's steps for five flashes: set the gas control thermostat knob to OFF, close the main gas supply, then have the gas control valve and thermostat replaced.
Count the flashes
ReversibleFive, with a pause between each set.
Turn the control knob to OFF
ReversibleAs A. O. Smith directs.
Shut the gas supply
ReversibleIf told to, and only at the valve.
Check the label
ReversibleModel, serial number and date.
Look for hot water elsewhere
ReversibleA second heater or the stove.
Call a licensed technician
ReversibleTo replace the control.
Model-specific
What is true of this model and not of its siblings
- A thermistor in the control
- The sensor that A. O. Smith refers to is a small temperature-sensitive resistor inside the gas control. It reads the water near the bottom of the tank.
- Lukewarm water as a clue
- A heater that has given lukewarm water for a few weeks before the code appeared suggests the sensor was drifting. A heater that stopped suddenly points toward a wire or an electronic failure.
- The repair is the control
- A. O. Smith's guidance for sensor failure is to replace the gas control valve and thermostat. The sensor is part of the unit, so it is not replaced alone.
- Sediment and age
- If the heater is many years old and has never been drained, a technician may suggest a flush and an anode check while the control is changed.
- Alternatives while you wait
- Heat water on the stove for dishes and use a kettle for washing. Do not use an oven or a gas burner to heat the room.
- Records
- Keep the invoice and the label photo for any warranty claim.
Stop boundary
When this stops being a self-service repair
- !Turn the gas control knob to OFF and the main gas supply OFF before any repair
- !If you smell gas, leave the building and call the gas utility from outside
- !Call a licensed plumber or gas technician for the control
Evidence ledger
Sources behind this answer
Exact questions
Common questions
What does 5 flashes mean on a AO Smith gas water heater?+
Sensor failure, which A. O. Smith lists for the temperature sensing inside the gas control.
What do five flashes mean on an A. O. Smith gas water heater?+
A sensor failure.
Why is my water lukewarm?+
The control cannot read the temperature properly.
Does a flush help?+
It may help with sediment but not a failed sensor.
Is the heater covered by warranty?+
Check the date on its label.