Came out to call for a furnace not heating properly. Customer stated that it stopped working last night and hasn’t really been working since. I checked the system over and found the heat drain on horizontal 90% furnace partially frozen. I sucked the standing water out of the line to get the system running but it only worked for 5-7 minutes. Unfortunately due to the weather, the line has frozen up, and I have no capability of unthawing the line at this time. Customer is going to buy some heating wrap to wrap the pipe to get it to thaw out.