State Industries STC-077 Pressure Switch Performance, Take AIR and GAS Pressure Readings

S U F 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	26	State Water Heaters
STC-077		Ashland City, Tennessee © 2004