Lennox furnace error code 66

Sometimes these furnace errors can be frustrating to figure out, and without the right experience, anyone can feel lost. This is where ARES Heat comes into play.

ARES Heat wants to make every customer feel at ease with their Lennox heating equipment by providing professional furnace repair service and giving homeowners customer support that they can’t find anywhere else.

Lennox furnaces are becoming increasingly efficient and sophisticated, but sometimes these modern devices can lead to a malfunction. In this case, we will diagnose an error code 66, a “System Fan 1 Insufficient Electric” error.

The problem may be due to the wiring or a blocked duct, so it’s very important to follow the carefully designed procedure when diagnosing this Lennox furnace with error code 66.

The wireless sensor on the Lennox evaporator sends periodic status IDs (sometimes at randomized intervals for security purposes) to the control board about the furnace’s internal and external temperature, humidity, and airflow rate. This data is compared with user-inputted information of desired cooling output and it decides if more or less cold air needs to be blown into your home.

For that to happen, one thing must happen: The data has to first reach the control panel. If a system communication has been shut down on purpose or due to a power failure – then no data will proceed any further.

Error Code 66 occurs if a major component has failed which is beyond the scope of the Lennox furnace protection system to control.  This code means someone is likely qualified to diagnose and repair the problem usually locally at your home or organization. While reading through our troubleshooting charts listed on the back of the installation and service manual, will give you a general idea of what could be wrong with the system.

Lennox states that the 66 error is “cannot communicate with the thermostat.” The exact problem more often than not involves a bad thermostat.


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