AO Smith 310 series condensing tankless error code 32
Temperature sensor open or shorted
Quick answer
On AO Smith 310 series condensing tankless, 32 is a fault. It means temperature sensor open or shorted. A first thing to check: Scale and sediment coated on the thermistors in the water circuit.
- 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
- Find the isolation valve upstream of the unit and the cold water supply, then isolate and drain the appliance as the manual describes before touching any sensor.
What 32 means on this model
The temperature sensors in the water circuit are reporting a resistance the control does not consider possible, which means the circuit is open or shorted rather than simply reading high or low. Scale on the sensors is the common cause, and it does the same job in a tankless unit as it does in a tank.
Symptoms you will notice
- Code appears on demand for hot water or during a self-check
- Outlet temperature swings or reads incorrectly on the remote
- Unit shuts down without completing a heat cycle
- Water comes out unusually hot or unusually cold at the fixtures
- Code returns quickly after a water filter service
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:
- Scale and sediment coated on the thermistors in the water circuit
- Thermistor connector unplugged, corroded, or pushed on partway
- Wiring between the sensors and the board chafed or broken
- Debris or a insect nest inside the sensor fitting
- A failed thermistor that has drifted out of its expected range
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.
- Find the isolation valve upstream of the unit and the cold water supply, then isolate and drain the appliance as the manual describes before touching any sensor.
- Once drained, look at the sensor tips through the water inlet opening and note any scale, grey deposit, or green corrosion.
- Reseat every thermistor connector firmly and check that each one clicks into a full stop.
- Follow the sensor wires back to the board and look for a break, a pinched section, or a connector that is not fully latched.
Do not do these
- ×Do not probe or touch a thermistor with power on, and do not measure sensor resistance with the unit still connected to the mains.
- ×Do not scrape a scale deposit off a sensor with a blade. A scratched sensor element reads wrong even when it looks clean.
- ×Do not skip draining. Opening the circuit with pressure behind it puts scalding water in the room.
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.
Descaling with a pump and neutraliser is a common homeowner or maintenance task if the unit is a standard tankless with a service valve. Electrical resistance checks and thermistor replacement are a technician job.
What it costs to fix
Parts
Thermistor $35 to $120 each. Descaling kit and filter $40 to $90.
Labor
One to two hours to isolate, drain, clean, and refit the sensors. Add time for a full descale of the heat exchanger.
DIY or technician
Descaling with a pump and neutraliser is a common homeowner or maintenance task if the unit is a standard tankless with a service valve. Electrical resistance checks and thermistor replacement are a technician job.
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
- Models in scope
- AO Smith 310 series condensing tankless
- 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.