A.O. Smith fault code S04
Fault code S04 on an A.O. Smith water heater (including ADMR) means: Flue gas sensor is not (properly) connected. Reset the appliance once. If the code comes back, a part is usually faulty, often a temperature sensor. You can check the water pressure and settings yourself; leave work on gas-carrying parts to a certified gas engineer.
After a safety alert (gas, flue gas, combustion), reset no more than once and call in a certified gas engineer. If you smell gas, call your national gas emergency number or 112 immediately.
Cause
Fault code S04 on an A.O. Smith water heater indicates: Flue gas sensor is not (properly) connected.
Applies to
A.O. Smith ADMR, 115, 135, 40, 50, 60, 80, 90.
Fault code S04 on other A.O. Smith series
The same code does not mean the same thing on every series. Check the rating plate to see which series you have:
- S04 on ADMR, 115, 135, 40, 50, 60: Defective flue gas sensor.
- S04 on ADMR, 115, 135, 40, 50, 60: Broken cable.
- S04 on BFC, 100, 120, 28, 30, 50: Dummy is not (properly) connected.
- S04 on BFC, 100, 120, 28, 30, 50: Defective dummy.
Matching parts
A.O. Smith parts are available from Instalpunt; shipping to EU countries from €17.95 (€24.95 for more distant countries), usually 3–5 working days.
Based on the cause, these original A.O. Smith parts fit (always check the type number of your appliance):
- A.O. Smith sensor NTC assy € 57.50
- A.O. Smith temperature sensor for e.g. ADMR 115 0300222001(S) € 92.78
- A.O. Smith TTB sensor 0303316(S) € 139.83
Further reading on this cause
Other A.O. Smith codes with the same cause
- 045 — Damaged wiring and/or defective sensor.
- 047 — Short circuit in the sensor circuit.
- 502 — Sensor fault: Sensor is not (correctly) connected.
- 503 — Sensor fault: Sensor is not (correctly) connected.
- 504 — Sensor fault: Damaged wiring and/or defective sensor.
- 512 — Sensor fault: Short circuit in the sensor circuit.
Fix it yourself or call an engineer?
Always consult the manual for your appliance and work safely. If in doubt or if the fault comes back, call in a qualified professional. A question about a part? Write to us at info@instalpunt.nl.
Frequently asked questions
What does A.O. Smith water heater fault code S04 mean?
Flue gas sensor is not (properly) connected.
How do I fix fault code S04 on an A.O. Smith water heater?
First check the cause described above. Then restart the appliance using the reset button. If the message comes back, a part usually needs replacing or the fault needs to be repaired by a qualified professional.
Which parts do I need for A.O. Smith fault code S04?
That depends on the exact cause. In the A.O. Smith parts overview at Instalpunt you will find the current price and stock for each part.
Can I fix fault code S04 myself?
You can reset the appliance and check things like the water pressure or settings yourself. Work on gas-carrying parts must be left to a certified gas engineer.
All A.O. Smith water heater faults and codes at a glance →