My heat was working fine until I got a manifold gasket put on

Hello, There are a few things that come to mind without seeing the vehicle in person: -The wrong gasket was used, and it is cutting off supply to the heater core (may or may not be possible) -The coolant is not filled completely, so there is not enough coolant to fill the heater core -The fuse for the blend door actuator is blown -The blend door actuator may have failed at a coincidental time -Something was dropped into the cooling system while it was open, so it now plugs the heater core That sure is a long list, but before you decide which route to take, narrow the problem down to one location. If the heater hoses going from the engine to the heater core are both hot, the issue is inside the cabin (they go in through the firewall). If one or both of those hoses are cold, the issue is in the engine bay or heater core.