Concur...from what I have read the "improved' sail switch is the same as the old one but with a different base mount [82 vs 81]....hence, it seems logical to assume that debris [belly button lint
] inhibits the sail switch movement thus it does not make electrical connection and start ignition of furnace. Lower elevations have higher air density and perhaps that increase air mass will move a slightly compromised [clogged] sail switch....
Has anyone actually taken out a sail switch that "failed" to start a furnace and confirmed that the circuit [electrical contact] was defective therefore stopping the electrical furnace starting signal?