Troubleshooting
HEATING SEQUENCE OF OPERATION WITH
NOTE − THIS FURNACE FUNCTIONS WITH TWO INDEDPENDENTLY CONTROLLED HEAT SECTIONS. THE GRAY BOXES INDICATE COMPONENTS WHICH EFFECT BOTH HEAT SECTIONS SIMULTANEOUSLY.
NORMAL HEATING MODE
POWER ON
THERMOSTAT CALLS FOR HEAT
(W1 ENERGIZED)
K13 RELAY ENERIZED.
A3 (A12) IGNITION CONTROL LED ON.
IS THE S10 (S99) HIGH LIMIT CLOSED?
YES
IS THE S47 (S69) ROLLOUT SWITCH CLOSED?
YES
IS THE B6 (B15) COMBUSTION
AIR BLOWER ON?
YES
IS THE S18 (S45) COMBUSTION AIR BLOWER PROVING SWITCH CLOSED?
YES
B6 (B15) COMBUSTION AIR BLOWER
PREPURGE FOR 30 SECS.
8 SEC TRIAL FOR IGNITION − START IGNITION TRAIL, GV1 (GV3) GAS VALVE OPENS ON LOW HEAT. IS FLAME SENSED WITHIN 8 SECS?
YES
K56 (K57) RELAY ENERGIZED. K25 CIRCUIT BOARD ENERGIZED. SYSTEM BLOWERS ON AFTER 45 SEC DELAY.
YES 
FLAME SENSE OK?
YES
CONTINUED NEXT PAGE
ABNORMAL HEATING MODE
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| NO | DETERMINE WHY |
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| S10 (S99) HIGH LIMIT OPEN. |
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| NO | CHECK VENTING SYSTEM |
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| OPERATION/BLOCKAGE BEFORE |
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| RESETTING THE |
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| (S69) ROLLOUT SWITCH. |
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| NO | CHECK K13−1 CONTACT OPERATION AND |
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| WIRING TO B6 (B15) COMBUSTION AIR |
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| BLOWER? |
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| NO | CHECK SENSING TUBE FOR BLOCKAGE |
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| AND S18 (S45) SWITCH FOR PROPER |
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| OPERATION. |
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| NO | |
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| GV1 (GV3) GAS VALVE CLOSED, SPARK | |||
NO | OFF. INCREMENT TRAIL REGISTER. | ||||
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| .5 SEC. ON AND 2.5 SEC. OFF. ARE THE | |||
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| THREE TRIALS COMPLETE? | |||
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| YES |
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LOCKOUT OCCURS. TO RESET A3 (A12)
IGNITION CONTROL MOVE THERMOSTAT
SWITCH FROM HEAT TO OFF TO HEAT.
NO
CHECK BELT.
CHECK RELAYS.
NO
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