A.O. Smith Error Code E5: Communication Error

Severity
Warning
Type
digital display
Estimated repair cost: $300 — $650 (parts + labor)
Warning: The water heater has lost communication with one or more of its components and has shut down. You will not have hot water until this is resolved.

How to Fix A.O. Smith Code E5

  1. Step 1: Check the power to the unit. Make sure the water heater is plugged in securely or that the breaker hasn't tripped. Reset the breaker if necessary.
  2. Step 2: If you have a remote controller, try removing and reinserting the batteries. Sometimes a simple reset can restore communication.
  3. Step 3: If the error persists after these steps, contact a qualified HVAC technician to diagnose and repair the communication issue.

How to Reset A.O. Smith Code E5

  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 E5 Mean?

The E5 error code on your A.O. Smith tankless water heater indicates a communication problem between the main control board and another component, most often the remote controller or the display panel. Think of it like a dropped call – the different parts of the unit can't talk to each other. This communication breakdown prevents the water heater from operating safely and efficiently, so it shuts down. It's important to address this promptly to restore hot water and prevent potential damage to the unit. This error could stem from a loose wire, a faulty communication cable, or a problem with one of the control boards themselves. Sometimes, power fluctuations can also cause this error. Because multiple components could be at fault, diagnosing the root cause requires some electrical testing. It's not something you can easily fix without the right tools and knowledge.

Common Causes

  • Loose or damaged communication wiring between the main control board and the remote controller/display panel.
  • Faulty remote controller or display panel.
  • Defective main control board.
  • Power surge or electrical interference affecting the communication circuit.

Diagnostic Steps

If... Check Expected
Unit displays E5 error Check the communication wiring between the main control board and the remote controller/display panel for loose connections or damage. Wiring is securely connected and shows no signs of damage (fraying, corrosion).
Wiring appears intact Using a multimeter, test the communication wires for continuity. Continuity exists between the corresponding terminals on the main control board and the remote controller/display panel.
Continuity is good Measure the voltage at the communication terminals on the main control board. Voltage reading within the manufacturer's specified range (typically 5-12 VDC).
Voltage is outside range Inspect the main control board for signs of damage (burnt components, corrosion). Control board appears undamaged.

Applicable A.O. Smith Models

Replacement Parts

Part OEM Number Est. Cost Where to Buy
Main Control Board — — —
Remote Controller — — —
Display Panel — — —

Related Codes on Same Models

Other codes that affect the same A.O. Smith model families as E5.

Code Description Severity
E06 Flammable Vapor Detection Critical
E1 Thermistor Failure Warning
E2 Dry Fire Protection Warning
E3 Sensor Fault Warning
E4 High Temperature Cutoff Critical
ECO Emergency Cutoff Critical
LOC Controls Locked Warning
LWR Lower Element Fault Warning
UPR Upper Element Fault Warning