A.O. Smith Error Code E2: Dry Fire Protection

Severity
Warning
Type
digital display
Estimated repair cost: $150 — $350 (parts + labor)
Warning: Your A.O. Smith water heater has shut down due to a potential dry-fire condition. This means the unit detected overheating, likely due to insufficient water flow. You may be without hot water until the issue is resolved.

How to Fix A.O. Smith Code E2

  1. Step 1: Check that the main water supply valve to the house and the shut-off valves to the water heater are fully open.
  2. Step 2: Inspect the inlet water filter (if equipped) and clean it if it's clogged. The filter is usually located on the cold water inlet line to the unit.
  3. Step 3: Try resetting the water heater by turning it off and then back on. Some models have a reset button. If the error reappears, call a qualified technician.

How to Reset A.O. Smith Code E2

  1. Turn off the unit using the power button on the front panel.
  2. Turn off the gas supply valve.
  3. Turn off the circuit breaker supplying power to the unit. Wait 30 seconds.
  4. Restore power at the breaker, then open the gas valve.
  5. Turn the unit back on. If the error returns, the underlying issue needs repair.

Resetting clears the code from the display but does not fix the underlying fault. If the code returns after reset, proceed to the diagnostic steps above.

What Does A.O. Smith Error Code E2 Mean?

The E2 error code on your A.O. Smith tankless water heater indicates a 'Dry Fire Protection' lockout. This safety feature is triggered when the unit senses the burner is firing without adequate water flow to cool it. The heater's control board monitors temperature sensors, and if the temperature rises too rapidly or exceeds a set limit, it assumes a dry-fire condition and shuts down the unit to prevent damage. This is important because running a tankless water heater without sufficient water flow can cause the heat exchanger to overheat and potentially crack or rupture. A cracked heat exchanger can lead to water leaks and, in some cases, carbon monoxide production if combustion gases are not properly vented. The E2 error is a protective measure to prevent these issues. The unit will remain locked out until the problem is resolved and the error is cleared.

Common Causes

  • Low water pressure or flow rate to the unit.
  • A blockage in the water inlet filter or supply lines.
  • Air trapped in the heat exchanger.
  • Faulty flow sensor or thermistor.
  • Scale buildup inside the heat exchanger restricting water flow.

Diagnostic Steps

If... Check Expected
Unit displays E2 error Measure incoming water flow rate Minimum flow rate specified in the A.O. Smith manual (typically 0.5-1.0 GPM)
Low flow rate observed Inspect inlet water filter for debris Filter is clean and unobstructed
Flow rate is adequate but E2 persists Check thermistor resistance at the heat exchanger Resistance matches the temperature/resistance chart in the service manual
Thermistor checks out Inspect the flow sensor for proper operation using a multimeter Continuity changes as water flows through the unit

Applicable A.O. Smith Models

Replacement Parts

Part OEM Number Est. Cost Where to Buy
Flow Sensor — — —
Inlet Water Filter — — —
Thermistor — — —

Related Codes on Same Models

Other codes that affect the same A.O. Smith model families as E2.

Code Description Severity
E06 Flammable Vapor Detection Critical
E1 Thermistor Failure Warning
E3 Sensor Fault Warning
E4 High Temperature Cutoff Critical
E5 Communication Error Warning
ECO Emergency Cutoff Critical
LOC Controls Locked Warning
LWR Lower Element Fault Warning
UPR Upper Element Fault Warning