My thermostats says outdoor unit communication fault. Outdoor unit control board has no led green or yellow lights. Outdoor unit has 240 vaults and the control board has 24 colts. Aux heat works but the heat pump doesn't. Any ideas? Could it be the thermostat?

Could be any number of causes. These Infinity systems are notorious for communication errors. If you Google Carrier Infinity communication errors, I'd wager you'd get lots of hits.