Amana AMVC960803BN Error Code EC4: Equipment Relay Module Missing

What Does Code EC4 Mean?

The communicating Amana AMVC960803BN can be configured to work with an external equipment relay module. This module provides the relay contacts the system uses to switch outside equipment such as a heat pump or air conditioner, and the integrated control module expects to see it on the ComfortNet system when the configuration calls for one. Code EC4 is raised when that expected equipment relay module is not detected.

Amana rates EC4 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 equipment that the missing relay module was supposed to switch cannot be commanded while the alarm is active.

EC4 is best understood as one of a pair with EC5. EC4 is the equipment relay module (for major equipment like a heat pump or AC); EC5 is the accessory relay module (for accessories like a humidifier or ventilator). Both are "expected module not detected" alarms. They are different 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 involve a device that was talking and stopped, whereas EC4 means the expected module was never found.

Because EC4 is about a module the system was told to expect, it commonly traces back to a 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 equipment relay module
• Equipment that the module switches, such as a heat pump or air conditioner, does not respond
• The furnace continues to deliver heat normally
• The integrated control module's 7-segment display shows EC4
• The code appeared after equipment was added, removed, or the system was reconfigured

Common Causes

How This Is Diagnosed

A technician first confirms whether an equipment 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 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:

• The heat pump or air conditioner controlled through the equipment relay module will not operate
• EC4 persists after the relay module and its connections have been checked
• EC4 appeared after equipment was added, removed, or the system was reconfigured, suggesting a setup mismatch

✓ Verified against manufacturer service manual — March 2026