How critical

Techman

is the positioning of the gas inlet pressure sensing switch ? For the past 4 years @ the 1st startup of heat the customer called for a lack of heat.I show up w/ a smile , remove the cover on the horizontal gas fired (LP) furnace,set the t'stat to call for heat &the unit  it starts and runs w/o a problem until the next season.Finally this season I happen to catch the lable on the inlet press sw. that states the bellows is for horizontal use.The installer repositioned the inlet press sw. to accomidate the use of a corrigated flexible gas line w/ the big 6 sided nut. &. the press sw. was remounted w/ the bellows in the vertical position.I will repipe and wait until next October.