I have an oil furnace with an indirect water heater attached. Recently my water heater went bad (I believe it was the coil) I had a plumber come and replace the water heater, and while he was there tune-up my furnace (clean nozzle, etc)

The next morning NO HEAT. Plumber was away for the weekend and could not be reached. I eventually called my oil company who determined it was not firing. After checking and replacing the ignitor still not firing, so the relay was replaced too. That resolved the problem.

Could something the original plumber have done during the tune-up / water heater replacement have caused the bad ignitor / relay?

Thanks
John

Yeah, he looked at them cross eyed. It is all too common for something that worked fine until disturbed the least bit, to then fail. Chances are, the parts were old and may have failed before long without the plumber.