Armstrong Air Return Air Temperature Sensor Fault

Armstrong Air communicating thermostat displays E4; system may shut down or limit capacity.

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

Possible Causes

Open or shorted return air sensor, Loose sensor wiring, Sensor damaged by filter access or service

Steps to check:

Locate return air sensor: Typically mounted in the return duct or near the furnace return opening.
Inspect sensor and wiring: Ensure the sensor is firmly mounted and wires are not pinched or cut.
Test sensor: With power off, measure resistance and compare to Armstrong Air specifications. Replace if out of range.
Secure sensor: After replacement, ensure the sensor is not in direct line of sight of the heat exchanger or supply air to avoid false readings.

Medium 3/5

Return Air Temperature Sensor

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