Lennox iComfort alerts 10, 31 and 39 that keep coming back: tracing intermittent faults without swapping parts

What Does Error 10, 31, 39 Mean?

Only one of the three is a communication code. Alert 31 reports that a component has not communicated with the thermostat for more than three minutes, and Lennox documents it as clearing once communication is restored. Alert 10 reports that an unknown device was found on the bus and needs configuring, not repairing. Alert 39 is a consequence: the system could not turn cooling on for more than 45 minutes, so it takes itself off-line for 60 minutes and retries. Replacing a control to chase 39 replaces the wrong thing. Applies to: Lennox communicating systems on iComfort S30, E30 and compatible displays, covering furnaces, air handlers, outdoor units, equipment interface modules and iHarmony zoning These entries come from the Lennox residential communicating systems alert table used with iComfort S30 and E30 displays. Lennox equipment running on a conventional 24 volt thermostat does not use this table, and legacy control-board flash patterns on the same appliance carry unrelated meanings. Owner-safe checks: Record the date, time and outdoor conditions each time an alert appears, and keep the list rather than clearing it. | Look for standing water or a slow drain at the indoor unit, because a float switch in series with the R terminal interrupts communication when it lifts. | Photograph any seven-segment display on the equipment, including a double horizontal line, before power is interrupted. Qualified technician: Voltage and continuity measurement at a communicating control is energised low-voltage work for a qualified technician. | Reconfiguration through the installer control center, and any isolation of devices on the bus one at a time, belongs to the installing contractor.