AO Smith Water Heater E5 Error — Communication Fault Fix

What Does This Error Mean?

E5 is a communication fault between the main control board and another component — typically the user display, the heat pump module (Voltex hybrid), or the gas valve module.
Connections shake loose over years from heating/cooling cycles or a single jolt of bad weather.
A power cycle clears about half of E5 codes; the rest need a plumber to reseat or replace a connector.

Affected Models

AO Smith Vertex
AO Smith Voltex hybrid
AO Smith Signature Premier
AO Smith ProLine XE

Common Causes

Communication cable loose between main board and display
Heat pump module disconnected (Voltex hybrid models)
Gas valve communication wire failed
Power surge corrupted the EEPROM on a board
Control board itself failed

How to Fix It

Power-cycle the unit.

Cut the breaker (electric) or gas valve and battery (gas) for 5 minutes.
Restore power.
Wait for the unit to fully boot — the display should show normal status.
If E5 doesn't return within 10 minutes, the cycle was successful.
Check the display and hood for damage.

Look at the user display panel.
Any cracks?
Any signs of moisture or burn marks?
If the display looks damaged, that's likely your E5 source.
Note for the plumber and avoid water near the unit until repaired.
On Voltex hybrid models, check the heat pump module.

If you have a hybrid (heat pump) model, look at the top of the unit where the heat pump sits.
Listen for the fan running during a heating cycle.
If the fan is silent and E5 is showing, the heat pump module has lost comms with the main board.
Don't open the unit yourself.

The control board lives behind sealed panels.
Opening means working with mains voltage on the controller side and possibly the gas valve.
Save it for the plumber.
They have the test harnesses to confirm the fault before swapping parts.
Call a licensed plumber.

Bring your model number, serial number, and how long the heater has been installed.
Most E5 codes are loose connectors (10-minute fix once on site) or a failed display module (50–100 USD parts).
A failed control board is the worst case (200–400 USD parts).

Frequently Asked Questions

Will my hot water work with E5 showing?

Sometimes yes, sometimes no — depends on which subsystem lost comms.
If it's the display, the heater may run fine but you can't change the temperature setting.
If it's the heat pump or gas valve, no heating will happen.
Either way, fix it within a few days.

Can a power surge cause E5?

Yes — and it's one of the more common triggers in storm-prone areas.
The control board's communication chip is sensitive to voltage spikes.
If your area sees frequent outages, ask the plumber about adding a small surge protector at the unit's branch circuit — cheap insurance.