Air pressure switch technical bulletins TB-A023-06 and TB-S023-06 explain air pressure switch construction and test procedures in detail. These technical bulletins are available on the manufacturers web site or by calling the technical support phone number shown on the water heater labeling. Construction and types of air pressure switches used on the water heater covered in this Service Manual are shown below.
The water heater covered in this Service Manual is factory equipped with three air pressure switches. These switches are used to provide verification or prove electrically that the blower is running and that the vent and intake air pipes are not blocked or restricted. The switches are located on the top of the water heater as shown in the illustration below.
• BLOWER PROVER SWITCH
normally open contacts – close on a rise in pressure
• BLOCKED INTAKE SWITCH
normally closed contacts – open on a fall in pressure
• BLOCKED EXHAUST SWITCH
normally closed contacts – open on a rise in pressure
All switches have SPST(single pole single throw) contacts.
These switches monitor air pressure through plastic sensing tubes from three different sensing ports on the water heater. The Blower Prover switch monitors pressure from the blower’s outlet flange. The Blocked Intake switch monitors pressure from the blower’s intake air connection fitting. The Blocked Exhaust switch monitors pressure from the exhaust/vent connection elbow on the bottom of the water heater. See the images below.