Can a C wire be added to an old Teledyne Laars JVT-100C boiler?
Yes you can, on your boiler there is a transformer above the gas valve. One terminal is the 24 v supply and the other is the common. It's not always easy to identify which is which. The process involves connecting one side of the secondary to the L2 (neutral) and checking if voltage is additive or subtractive. Hopefully it's identified. It's much easier that way.