The ticking sound is the electronic igniter doing its thing. If the heater doesnt fire,its usually clogged orifices. On a heater that old, it is not a surprise. Likely causes are rust or cobwebs in the gas manifold's orifices. Not a DYI job on a heater that old. It owes you nothing. Do not spend a lot of money and effort on it. Be prepared to replace it. IF you do fix it, expect something else soon to break. And then again and again.... Scott

The gas supply would have to be virtually non existant for a small draw such a pilot not to work. If this is a new installation make sure that the gas valve is on inside the heater (kinda duh! but it's happened to me). The Ruud, Rheem, and Raypak heaters are all the same. Once there is a call for heat the heater attempts to light the pilot with its spark ignition. You have the spark system energizing and making a pulsing buzzing sound. BZZT pause BZZT paust etc. Down below on the actual pilot you should see the spark arcing across the pilot. If it is arcing and there is no flame; the problem is either, the pilot orifice is clogged (likely), the ignition control is not telling the gas valve to open (less likely), or the pilot solenoid system on the gas valve has failed (even less unlikely on a newer heater). Now lets say that the pilot arced, and barely lit. This is more than likely a clogged pilot orifice. If the pilot lit and there is a reasonable sized flame, but the main valve doesnt open there is more than likely a problem with the rectification system, or the ignition controller. It is extremely difficult to diagnose a heater across the net, but I am somewhat surprised and not surprised that an hvac technician could not figure out the root of a problem so simple. This is not something that you need to be an engineer or have sophisticated instrumentation to figure out. Sometimes there is some bizarro problems but the ones I listed above are pretty much the only ones that you would regularly see.

Any other fried part might cause an issue. If a fan was shorted, for example, and there might be another board somewhere. Do you have the service manual for it?

OK....I'm gonna pull the trigger on the pc board. However, I'm not sure which one to buy and I know if I order it online, and it's wrong, I won't be able to return it. I have a Raypak model# C-335A-EN Serial# o786o25242 The issue is that there are 2 possibilities. Part #005086B looks like my board but doesn't seem to have 8 terminals like mine. #005089B is supposed to have 8 terminals like mine but is a sealed unit (mine is open) Anybody have experience with this model? Raypak won't talk to me because I'm not a dealer. Thanks, Bruce