Thermo Products CHX3-125N, CDX3-75N, CHX3-75N Is Inducer Running On Low Speed? Yes Does The Hot

All installations and services must be performed by qualified service personnel.

IS INDUCER RUNNING ON LOW SPEED?

YES

DOES THE HOT

SURFACE IGNITOR ENERGIZE AND GLOW?

YES

NO

NO

CHECK CONTACTS ON LOW FIRE PRESSURE SWITCH AND FOR BLOCKAGE IN FLUE. IF OK, REPLACE DUAL PRESSURE SWITCH.

IS THERE VOLTAGE ACROSS

HOT SURFACE IGNITOR

TERMINALS "IGN" & "IGN N" AT THE 50V51-843 CONTROL AFTER 17 SECOND PREPURGE?

YES

CHECK WIRING TO HOT

SURFACE IGNITOR AND

IF OK, REPLACE HOT

SURFACE IGNITOR

ASSEMBLY

	REPLACE THE
	50V51-843 CONTROL.
		YES
	IS THE HIGH LIMIT,
NO	ROLL-OUT LIMIT, AND
	AUX LIMIT ON
	(CDX MODELS)
	SWITCHES CLOSED?

NO

IF HIGH LIMIT OR

AUX LIMIT OPEN CHECK

FOR RESTRICTED

FILTERS OR DUCT WORK

IF ROLL-OUT SWITCH

OPEN INSPECT FLUE FOR

RESTRICTIONS.

AFTER HOT SURFACE IGNITOR WARM-UP, DOES GAS VALVE OPEN?

YES

AFTER GAS VALVE

OPENS, DO THE

BURNERS IGNITE?

YES

NO

NO

CHECK ACROSS "MVL" AND
"MV COM" TERMINALS ON
50V51-843 CONTROL FOR 24		NO
VOLTS DURING THE 4 SECOND
FLAME PROVING PERIOD
AFTER IGNITOR WARM-UP.
IS THERE 24 VOLTS?
	YES

IS COLLECTOR BOX NO

PRESSURE SWITCH CLOSED?

YES

CHECK WIRING TO GAS

VALVE AND IF OK,

REPLACE GAS VALVE.

CHECK FOR PROPER LINE

AND MANIFOLD PRESSURE.

REFERENCE GAS PRESSURE

CHART PAGE 31.

OK

REPLACE THE

50V51-843 CONTROL.

CHECK DRAIN FOR BLOCKAGE WATER TRAPPED IN HOSE, REPLACE SWITCH.

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