Ambient room air pressure, Pressure switch performance, Take air and gas pressure readings – A.O. Smith 960 through 967 User Manual

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BTH S E R V I C E H A N D B O O K

T R O U B L E S H O O T I N G

PRESSURE SWITCH PERFORMANCE

STEP 9A

TAKE AIR AND GAS PRESSURE READINGS.

Blower prover and blocked outlet pressure

Blower inlet pressure

STEP 9A: CHECK PRESSURE AT SENSING PORTS ON BURNER, BLOWER INLET AND GAS
VALVE.

Condition:

• All wires are reconnected to all pressure switches.

• On/Off switch is on.

• Call for heat is activated.

• Blower is running during trial for ignition.

Remove the air pressure sensing tubes from the sensing ports on the blower inlet and the burner.
Using a digital manometer take a pressure reading with the blower running during a call for heat at
both of these sensing ports. Take a supply gas pressure reading on the inlet side of the gas valve

as outlined in Step 13.

Record all 3 pressure readings and have them on hand. Continue to Step 9B.

AMBIENT ROOM AIR PRESSURE

N O T E : One side of the internal diaphragms on these pressure switches are vented to the
room atmosphere. Due to this construction a negative or positive room air pressure can cause

erratic switch operation and the water heater to shut down. If you suspect a pressure imbalance

between the equipment room and the outdoor atmosphere, “zero” or calibrate your digital
manometer to the equipment room ambient air pressure. With the manometer still on and

calibrated to the equipment room air pressure take the manometer outdoors. If the pressure

reading changes significantly you may have a pressure imbalance between the equipment room

and the outdoor atmosphere. This pressure imbalance may need to be corrected before the water

heater will operate properly.

Insure the combustion/make-up air openings into the equipment room are properly sized. Check for

leaks in ductwork on any nearby air handling equipment. If there is a kitchen vent hood installed in

the building, insure it is properly balanced. Missing or worn fan belts on make up air fans to vent

hoods can cause negative air pressure throughout the building.

Direct vent installations DO NOT eliminate this potential problem.

Technical Training Department

TC-044 Revision 6

This manual is related to the following products:

970 through 973 120