Aprilaire HVAC Error Code E5

E5 on an Aprilaire HVAC unit means the control board has detected a failure in the High Temperature Sensor thermistor circuit. The signal from the sensor is either open (no continuity) or shorted, making it impossible for the system to get a valid temperature reading. The unit will not operate normally until the fault is resolved. The most likely causes are a loose connector at the control board or a failed sensor.

It is not advisable to continue running the unit with an active E5 error. The High Temperature Sensor is a protective component that monitors for overheating conditions. Without a functioning sensor, the system lacks the ability to detect and respond to dangerously high temperatures, which could result in equipment damage or a safety hazard. Address the fault before resuming normal operation.

If the issue is only a loose connector, the repair cost is minimal, potentially just a service call fee ranging from around $75 to $150 depending on your area. If the High Temperature Sensor needs replacement, parts and labor together typically range from $100 to $300. If the Internal Control board is at fault, costs can rise to the $200 to $500 range or more, depending on the specific unit and labor rates in your region.

A knowledgeable DIYer comfortable working with electrical components can attempt the initial diagnostic steps. This involves turning the unit OFF, removing the side panel, insulation, and electrical box cover, then using a multimeter to measure resistance across the High Temperature Sensor connector terminals. If the issue is simply a loose connector, reseating it is straightforward. Replacing the sensor or the control board is a more involved repair and may be better handled by a qualified technician.

Simply resetting the unit by cycling power will not permanently clear the E5 error if the underlying fault still exists. The error will return as soon as the control board attempts to read the High Temperature Sensor signal and finds it open or shorted. The fault must be corrected, either by securing the connector or replacing the sensor, before the error will clear and stay cleared.