Furnace Gremlins get a Face!

This was one of those failures that can send you in circles for hours, especially with the furnace buried deep inside a cabinet and no exterior access door. It’s not an easy problem to test or even identify at first. The symptoms can easily mimic several other issues — sail switch dropout, a high-limit thermostat opening, or even a failing control board.

That’s what makes this guide so valuable: it puts a face to an otherwise invisible failure.

The key clue was what happened after the furnace initially ignited. About five minutes later it shut down, then attempted ignition two more times all without any smell of propane at the exhaust. That detail matters. The furnace was still trying to relight because the control board never recognized the actual failure condition.

If this had been a sail switch or high-limit issue, the furnace would typically keep the blower running without attempting another ignition cycle. Instead, the system behaved as if everything was normal, making this a true “ghost” failure.

These are the kinds of problems that make RV furnace diagnostics both frustrating and fascinating.