form_title= Tankless Water Heater form_header= Repair or install a tankless water heater in your home! Do you need a tankless water heater repaired or installed?*= () Repaired () Installed What size water heater do you need?*= _  What is your budget on the water heater?*= _ 
By make and model number.
Yes, the overhead heater controls do light up.
Don't know what vehicle you have but most HVAC controls operate from a vacuum supply from the engine. I would start with checking the vacuum supply connections under the hood. They could be cracked or disconnected.
Loosen the dash and pull out the complete heater box after you have disconnected the heater hose from the firewall...........
There may have been some water left in the heater core when you disconnected both hoses at the firewall. I can't think of any other explanation since there is no water circulating through the heater core.
The circuit is open. Wires could be disconnected/damaged or the heater element is burned out.
You have a vacuum line disconnected probably under the hood. The HVAC controls are operated by vacuum and when there is no vacuum it system goes into defrost mode.
Blocked heater core, faulty heater valve, disconnected connection to the heater valve.
To get to the bulb for lighting the heater controls, the front panel will have to be removed. Depending on the type of vehicle, the knobs might have to be popped off first. It is also possible on some vehicles to get to the lighting for the heater controls from under the dash.
The heater matrix, also known as a heater core, is usually replaced if found defective. They can be repaired, but is usually cost/performance prohibited.
Your heater core is leaking. It needs repaired or replaced.