The furnace sits ten months. Then it has to light.
Riverside furnaces live a strange life: idle from March through November collecting dust, then asked to fire flawlessly on the first cold night of December. That first-light moment is when the no-heat calls stack the board — and the failures are almost always the same cast: a hot-surface igniter that finally cracked, a flame sensor fouled with oxidation, a pressure switch that won’t prove, or a board that gave up over the summer.
The most common sequence failure has a two-dollar part at its heart. The flame sensor is a metal rod that proves the burner lit; when oxidation coats it, the furnace lights, can’t confirm the flame, and shuts down three seconds later — over and over. Cleaning or replacing it is fast and inexpensive. The pattern “lights then quits” points straight at it, which is why the sequence matters more than the part.
Age changes the conversation honestly here too. A fifteen-year-old furnace with a failed board sits at the repair-replace line, and the right answer depends on the heat exchanger — the part a crack turns into a safety issue. Every older furnace gets its exchanger inspected as part of the diagnostic, because that’s the finding that ends debates. If it’s sound, repair away; if it isn’t, you’ll see the photos and the reasoning.