Arrived to system off and flashing code for pressure open. Removed pressure switch hose from inducer port and water started flowing out of inducer port. Water is backing up the drain line and into the inducer causing the inducer port to be clogged not allowing the pressure switch to close. Removed hose at the collector box and tried to blow through drain line. Went outside to check drain line and found that it had frozen not allowing the system to drain properly. Told homeowner that I could try and melt the ice with a hairdryer but more than likely it will freeze again. Other option is to install a condensation pump and run it to the vent stack, told him we would get the estimate sent over to him. Drain line is still clogged.