Honeywell Thermostats: VisionPro IAQ
Re: Thermostat Shows Error 40
Some heat pumps have a diagnostic board that will flash a light or display "Error 40" at the thermostat when a fault condition occurs.
- Error Code 40 is displayed on a Honeywell VisionPro IAQ thermostat when it receives a 24V signal on the "L" terminal.
- The actual Honeywell description of a Code 40 is "Compressor not operating when it is supposed to be".
- This is typically associated with a fault from the outdoor unit.
Fault Codes:
- Any fault condition that activates the "L" terminal will cause an Error 40.
- In order to see the actual fault code you must visually check the outdoor unit control.
- Most fauts can be Reset by cycling power to the air handler.
- Some codes can be Reset by turning the thermostat System switch to "Off" for 30 seconds and back on.
What the Customer Should Do:
- Check/replace air filter.
- Check breakers.
- Reset the lockout by one of the reset methods mentioned above.
- Make sure the indoor blower is operating.
- Check the outdoor unit for any abnormal conditions.
- If Error Code 40 returns - have a technician check the equipment.