Despite their vintage of around 25 years, I can't find much fault with these Rheem/Ruud furnaces; the ones with the spark ignition and the burners welded into one unit. Under rare circumstances, the welds will fail, necessitating replacement of the furnace because these burners are no longer available. Other than that, if well cared for these will last a long time.One issue that I do find with these is not with the furnace itself, but the way it's worked on. I got a call from a consulting firm who had a competitor do a tune up and now the furnace was acting up. I drove over and the customer informed that the furnace was lighting intermittently. I noticed right away that the clips holding the burner assembly were missing and had been for some time. The wiring to the flame sensor was also worn and the ground wire wasn't hooked up either. The spark ignition module wasn't secured to the plate underneath and the neither was the plate to the cabinet. None of this was hooked up before the other tech started and it wasn't hooked up when he left either. So why did it work fine before he touched it and then started messing up afterward?
I fiddled with the wiring and got the furnace to light, and as soon as the main valve came on, the burner assembly jumped under the pressure. The flame sensor works with the ignition module and has to be grounded to the burners, which are grounded to everything else. When the tech removed the burners, he disrupted the precarious balance that was had despite the burners not being secured. He tried to wedge them back in, but Rheem put those clips in for good reason. I fabricated a clip to hold the burners down and secured all the wires. The furnace lit every time with no hesitation.
The moral of the story is if it came with it, put it back on. The last tech that worked with it was only guilty of being in too much of a hurry. The tech who installed the module should taken the ten minutes to check the integrity of the wiring and secured the parts after he was done . Furnaces are just as complex and as much a precision piece of equipment as cars, TVs or even computers. You wouldn't leave parts out of your car, computer, or TV but why would you leave a part out of something that could kill you at worst or leave you without heat? As much of a pain as it is, put it back together and when you see something that isn't right, at least tell the customer. I've made this mistake too and it's come back to bite me in the aft end. Mistakes are best learned second hand after all. Maranatha!