Originally Posted by harbortj
.... don't know whether to buy a whole control valve, or if I just need to adjust or replace the pilot electrode thingy.
I can't give you a real good answer as I have a DSI water heater, no pilot light but maybe I can get you started untill better minds prevail.
First, since it is a Sunline it may be safe to assume (dangerous word!) that it is an Atwood and most of them are similar. Before replacing anything you could try cleaning the gas jet(s) and make sure the pilot you get has a good flame. Next make sure the electrode thingy is over the flame and is getting heated, that tells the control board that there is a flame. I have heard that sometimes if there are bug nests in the main heat path the delay in igniting the main jet causes a "puff" (or worse) that can blow out the pilot light. Cleaning and blowing everything out with an air blast from a compressor, if you have one, may help.