Hi All:
I'm having trouble with my 20+ year-old Sears 867.762340 gas furnace.
About once a month, it will fail to ignite the burners. It just sits there with the vent blower running.
If I short out the contacts on the pressure switch, the burners start right up and everything works normally.
I've dismantled the relevant parts. Checked the gas vent from top and bottom; cleaned the rubber sensor tubes and checked them for leaks; cleaned the insides of the metal fittings to which they attach; checked the electrical connections to the pressure switch; and checked the pressure switch itself (it responds immediately to very light sucking and blowing on its input ports). Everything was squeaky clean as far as I could tell, and I didn't find anything wrong with any of the components.
After re-assembly, the old behavior is back. Furnace fails to start about once a month.
The only thing I can think of is that the switch contacts inside the pressure switch are worn or corroded, so they don't always close the circuit.
Before I sink $70 into a new pressure switch, does anyone have any ideas about what might else be causing this problem? And are the pressure switches known to wear out?
Your help greatly appreciated.
Pete