Cannot guess as to common failure on that model..
There is probably some sort of fuse in the low voltage supply, for UL. If it does not light up, the low voltage power supply is not working. You state that you have it connected per manual, so if it won't light, either it actually is not getting power, or else the low voltage (control) power supply is not working for some reason.
Check the wires. If possible, check for AC after the connections, (or DC on the bus) to verify that power is getting in.
Typically these are not at all economical to fix, unless you are sufficiently skilled to do it yourself correctly. If it is getting power and does not work, then "it's broke" unless you know how to fix it.