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 (CONTINUED)
STEP 9B
PRESSURE SWITCH CONTINUITY TEST — OPERATIONAL
SUF 240
ONLY
Air pressure switches | Low gas pressure switch |
STEP 9B: CHECK FOR CONTINUITY BETWEEN PRESSURE SWITCH TERMINALS WITH WIRES REMOVED AND BLOWER RUNNING.
Condition:
•All wires are disconnected from all pressure switches — ends are taped off.
•On/Off switch is on.
•Call for heat is activated.
•Blower is running during trial for ignition.
•Multimeter is set to lowest ohms scale.
The wires disconnected are energized with 24 VAC from the control board. Do not allow these wires to touch ground — use electrical tape to insulate wire connects during this test.
Check for continuity with an ohm meter between terminals on all pressure switches with the wires removed and the blower running during a trial for ignition. Restart the water heater as needed.
The pressure switches are wired together in a “series” circuit. For the water heater to continue to fire and satisfy a call for heat the control board must sense a closed pressure switch circuit.
IF… | THEN | |
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continuity is not present between terminals on | if the pressure recorded in Step 9A is within the value shown in | |
one or more pressure switches — the switch | the table for the switch contacts to remain closed — replace the | |
contacts are open. | pressure switch. | |
compare the pressure reading recorded in Step | if the pressure recorded in Step 9A is not within the value shown | |
9A to the value given for that switch in the table | in the table for the switch contacts to remain closed — check for/ | |
on page 34. | clear any restrictions in the vent and/or air intake piping, check | |
compare to value for correct Model and Series | for an excessive number of elbows or equivalent feet of pipe | |
used in the vent and/or air intake piping. | ||
number in table. | ||
check for/restore minimum supply gas pressure — Step13. | ||
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continuity is present. | continue to Step 10. | |
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State Water Heaters | 27 | Technical Training Department |
Ashland City, Tennessee © 2004 |
