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Model VSU Make-Up Air
®
Heater Does Not Operate (Direct Spark)
Does not attempt to light (No visible spark)
Troubleshooting
24 VAC between
terminals W1 and X?
Heat switch (S4) off.
Turn heat switch (S4) on.
Heat switch not wired.
Wire heat switch (S4).
24 VAC between
terminals 22 and 21?
Main transformer (TR2) defective.
Replace transformer.
24 VAC between
terminals 26 and 21?
(Optional) high/low gas pressure switch(es)
(PS3 and PS4) tripped.
Correct gas pressure and reset.
Reference: Start-Up - Direct Gas, Check the Pilot Gas Pressure, pg. 15
24 VAC between
terminals 24 and 21?
High limit (HLC1) tripped.
Reset, replace high limit (HLC1).
Check on cause of control loss.
Continuity between
terminals 26 and 27?
24 VAC between
terminals 23 and 21?
(Optional) inlet air sensor (TS4) holding.
Adjust TS4 setting.
Reference: Start-Up - Blower, Set-Up Optional Components, pg. 15
Heat relay (RH) defective.
Replace heat relay (RH).
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Airflow switch (PS2) holding for proper airflow.
Correct airflow across burner.
Reference: Start-Up - Direct Gas,
Check the Optional High and Low Gas Pressure Switches, pg. 15
Yes
At this time the heater should attempt to light.