Amana AMVC960803BN Error Code EC5: Accessory Relay Module Missing

What Does Code EC5 Mean?

The communicating Amana AMVC960803BN can be configured to work with an external accessory relay module. This module provides the relay contacts the system uses to switch comfort accessories such as a whole-home humidifier or a ventilator, and the integrated control module expects to see it on the ComfortNet system when the configuration calls for one. Code EC5 is raised when that expected accessory relay module is not detected.

Amana rates EC5 low severity because it is an informational configuration alarm rather than a combustion or gas-safety fault. The furnace itself typically keeps heating, but the accessory the missing relay module was supposed to switch cannot be commanded while the alarm is active.

EC5 is the companion of EC4. EC5 is the accessory relay module (for accessories like a humidifier or ventilator); EC4 is the equipment relay module (for major equipment like a heat pump or air conditioner). Both are "expected module not detected" alarms. They differ in kind from EC1, EC2, and EC3, which are lost-communication alarms for the ComfortNet thermostat/network, the external E-Module, and the Bluetooth phone-app module respectively — those describe a device that was communicating and dropped out, whereas EC5 means the expected module was never found.

Because EC5 is about a module the system was told to expect, it commonly traces back to an accessory relay module that is not installed, not connected, or has failed, or to a configuration that expects a module the system does not actually have.

What You'll Notice

• The ComfortNet thermostat reports a missing accessory relay module
• An accessory such as a humidifier or ventilator stops running or will not turn on
• The furnace continues to deliver heat normally
• The integrated control module's 7-segment display shows EC5
• The code appeared after an accessory was added, removed, or the system was reconfigured

Common Causes

How This Is Diagnosed

A technician first confirms whether an accessory relay module is actually supposed to be present for this installation, then checks that the module is installed, seated, and connected on the ComfortNet system. The wiring to the module and to the accessory it drives is inspected for loose or damaged connections, since a module that is present but not properly connected will not be detected.

If a module should exist but cannot be found, the technician determines whether it needs to be installed or replaced; if no such module belongs on the system, the configuration is corrected so the control no longer expects one. This is diagnostic context only, not a homeowner repair procedure.

When to Call a Professional

This code involves components that are not homeowner-serviceable, so have a licensed HVAC technician diagnose and repair it. Keep in mind:

• An accessory such as a humidifier or ventilator that runs through the relay module will not operate
• EC5 persists after the accessory relay module and its connections have been checked
• EC5 appeared after an accessory was added, removed, or the system was reconfigured, suggesting a setup mismatch

✓ Verified against manufacturer service manual — March 2026