Arrived to remedy an inoperable system. Upon inspection of the system found that the furnace would not operate and it was giving a fault code related to the pressure switch. This is a similar issue as yesterday. Performed diagnostic on the pressure switch and venting system. Found that even though the pressure switch is closing and trying to relay its signal, it is not a reliable signal. Without the control board receiving a reliable signal it will not allow the system to operate. Spoke with homeowner and with homeowners approval replaced the pressure switch. Tested system operations. Furnace is functioning properly at this time.