It's not a thermal overload. Rather, the bulb can light only after a spark is 'ignited.' If the ignition circuit has a problem, and the arc is not maintained ... the bulb goes out.
Then, the ballast will attempt to strike a new arc. It succeeds, the bulb lights again.
Should either part - bulb or ballast - be marginal, the bulb will cycle on and off.
As for myself, I always start with a known good bulb. Then I follow up with an 'in use' inspection. If the problem returns, it's time to replace the entire ballast assembly.
IMO, there's really no safe, practical way to repair a ballast on the pole. At best, you look like a bumbling fool as you spend hours and make multiple trips to fix the problem. Remember- just because, say, the capacitor tests as "ok" at the time you replace the igniter ... the entire ordeal may have damaged it, and it may fail in a few days.
Contractor law says my work has a one year guarantee. I'm not going to be able to charge for those return trips!
Last edited by renosteinke; 10/21/07 11:42 AM.