A. O. Smith · Voltex AL Smart / Signature 900 Standard (HPTS, HPS10)
A. O. Smith Voltex AL Smart / Signature 900 Standard (HPTS, HPS10) error code 003
Upper thermistor sensor failure
What it means
Upper thermistor sensor failure. Upper thermistor sensor is mounted to tank and located above upper element. NOTICE: The Control Assembly will go into Limp Mode 1 until the failure is corrected.
How it shows: with an alert icon flashing (also flashing red LED)
What A. O. Smith says to do
These steps involve electrical testing or parts replacement. A. O. Smith's manuals tell owners to leave that work to a qualified service technician.
1. Turn OFF electrical power at the breaker. 2. Check electrical connections at Control Assembly board. 3. If there are no issues with the wiring, replace the thermistor. 4. Turn ON electrical power at breaker.
The manual adds: "These instructions are brief and intended as guidance for a qualified person. If you lack the necessary skills to perform these procedures call the Technical Assistance Hotline which is listed on the water heater's warranty sheet for assistance." (Hybrid Electric Heat Pump Water Heater Installation Instructions and Use & Care Guide, 100379659_2000812395, page 27)
Last checked 2026-10-03.
Safety first
- WARNING! Working near an energized circuit can result in severe injury or death from electrical shock. (p.28)
- WARNING! When you are finished, be sure all covers are secured to reduce the risk of fire and electric shock. (p.28)
From the manufacturer's manual for this series.
The same code on other models
Codes mean different things on different heaters. Match the series to the model number on your rating label.
- A. O. Smith Voltex MAX / Signature 900 Premium (HPTA, HPA10): 003
- A. O. Smith Voltex 120V plug-in (HPTV, HPV10): 003
Other Voltex AL Smart / Signature 900 Standard (HPTS, HPS10) codes
- 001 (Dry-fire)
- 004 (Lower thermistor sensor failure)
- 006 (Internal Processor Error)
- 009 (Power supply voltage too low)
- 021 (Upper element circuit failure)
- 022 (Lower element circuit failure)
- 025 (Heat pump coil temperature sensor)
- 026 (Heat pump suction temperature sensor)
- 027 (Heat pump discharge temperature sensor)
- 028 (Ambient temperature sensor failure)
- 031 (Water leak)
- 044 (SAC anode depleted)
- 046 (Shut-off valve)
- 048 (Battery low energy)
- 080 (Air filter dirty)
- 081 (Condensate management)
- 083 (Compressor suction pressure too low)
- 084 (Compressor not functioning)
- 085 (Compressor discharge temperature too high)
- 086 (Fan speed feedback)
- HPO (Heat pump out of operating range)
- ICE (Heat pump defrost)
- CLR (Error code cleared)