Heater Does Not Operate (Direct Spark); Maintenance - Greenheck VSU Installation, Operation And Maintenance Manual

Troubleshooting

Heater Does Not Operate (Direct Spark)

Does not attempt to light (No visible spark)
24 VAC between
terminals W1 and X?
Yes
24 VAC between
terminals 22 and 21?
Yes
24 VAC between
terminals 23 and 21?
Yes
24 VAC between
terminals 24 and 21?
Yes
24 VAC between
terminals 26 and 21?
Yes
Continuity between
terminals 26 and 27?
Yes
®
No
No
No
(Optional) inlet air sensor (TS4) holding.
Reference: Start-Up - Blower, Set-Up Optional Components, pg. 15
No
No
(Optional) high/low gas pressure switch(es)
Reference: Start-Up - Direct Gas, Check the Pilot Gas Pressure, pg. 15
No
Airflow switch (PS2) holding for proper airflow.
Check the Optional High and Low Gas Pressure Switches, pg. 15
At this time the heater should attempt to light.
Heat switch (S4) off.
Turn heat switch (S4) on.
Heat switch not wired.
Wire heat switch (S4).
Main transformer (TR2) defective.
Replace transformer.
Adjust TS4 setting.
Heat relay (RH) defective.
Replace heat relay (RH).
High limit (HLC1) tripped.
Reset, replace high limit (HLC1).
Check on cause of control loss.
(PS3 and PS4) tripped.
Correct gas pressure and reset.
Correct airflow across burner.
Reference: Start-Up - Direct Gas,
Model VSU Make-Up Air 29