car service question

OK, as long as this thread is here, help me with this one:

Yesterday morning, my 2004 Ford Ranger truck overheated just a couple of miles from home and, by the time I limped into the driveway, ALL of the coolant was lost. Today, my son-in-law found the problem to be a cracked plastic part, called a heater control valve. He put a new one on, and the truck is now driveable. Only problem is I now have NO HEATER, and the CHECK ENGINE LIGHT is now on. Any ideas before I check it for any codes?

For what it's worth, here are mine:

1. The thermostat was ruined when the truck redlined, and it will have to be replaced.

2. Andy (my son-in-law) may have installed the new part improperly.

3. Something happened to the vacuum line connection to that heater valve (again, possibly when the new part was installed).