Aprilaire HVAC Error Code E6

The E6 code on an Aprilaire HVAC unit indicates a Low Temperature Sensor (Frost Sensor) thermistor failure. The Internal Control board has detected that the sensor signal is either open or shorted, meaning it is not receiving a valid temperature reading. This is most commonly caused by a loose connector at the control board or a sensor that has failed internally. The unit will not operate normally until the fault is resolved.

Running the unit with an active E6 code is not advisable. The Low Temperature Sensor is a frost protection device, and without a valid signal from it, the system cannot properly detect conditions that may lead to frost buildup on the coil. Operating the unit in this state could result in reduced efficiency, ice formation, or potential damage to the system. Address the fault before resuming normal operation.

Simply resetting the unit is unlikely to permanently clear the E6 code if an underlying fault exists. If the connector is loose, reseating it and then powering the unit back on may resolve the error. However, if the sensor has failed or wiring is damaged, the code will return because the Internal Control board will continue to detect an invalid signal. The root cause must be diagnosed and corrected for the error to clear and stay cleared.

A knowledgeable DIYer can perform the initial diagnostic steps, which involve turning the unit off, removing the side panel, insulation, and electrical box cover, and checking the sensor connector for a secure fit. If reseating the connector does not clear the code, testing sensor resistance with a multimeter is the next step. Replacing the thermistor or Internal Control board is also within reach for someone comfortable with HVAC electrical components, but if you are unsure about working with electrical systems, a qualified technician is recommended.

If the issue is simply a loose connector, the repair may cost little to nothing beyond a service call fee, which typically ranges from $75 to $150. If the Low Temperature Sensor thermistor needs to be replaced, parts and labor combined generally fall in the range of $100 to $300 depending on the technician and part availability. If the Internal Control board is determined to be faulty, costs will be higher, often in the $200 to $600 range including labor.